Subaru Ignition and Tune-Up Products

NGK V-Power spark plugs offer reliable performance and improved ignitability over standard nickel plugs. Engineered specifically for OE applications, the special V-cut nickel alloy center electrode and concave ground electrode of NGK’s V-Power spark plug

Product Features:

• ACTUAL OE or EQUIVALENT DESIGN: OEM quality construction nickel alloy center electrode with V-groove provides consistent performance
• RECOMMENDED USAGE: Best for vehicles with OE nickel alloy plugs, not recommended on vehicles with factory precious metal plugs
• NGK’s OE CERAMIC TECHNOLOGY: High grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal

NGK Iridium IX spark plugs are specifically designed for the performance enthusiast. Iridium IX provides outstanding acceleration, high fuel efficiency and durability. NGK Iridium IX plugs offer extreme ignitability and exceptional anti-fouling. Tapered cut ground electrode provides improved starting, idling and throttle response. The Iridium fine wire center electrode’s durability is six times harder than platinum. Iridium alloy’s extremely high melting point is perfect for today’s engines. For even greater performance consider upgrading to an NGK Ruthenium HX plug.

Product Features:

• SINGLE IRIDIUM TIP: Fine wire 0.6 millimeter iridium tip center electrode ensures high durability and a consistently stable spark
• IRIDIUM ALLOY CENTER ELECTRODE: Iridium’s density (6x that of platinum) and extremely high melting point is perfect for modern high efficiency engines
• TAPERED CUT GROUND ELECTRODE: Reduced quenching design produces outstanding ignitability, improved acceleration, fuel efficiency and durability
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• RECOMMENDED USAGE: Modified or high performance applications, or as an upgrade to OE nickel alloy spark plugs
• Outstanding Acceleration and High Fuel Efficiency: NGK Iridium IX spark plugs are engineered to deliver superior acceleration and enhanced fuel efficiency, making them ideal for performance enthusiasts.
• Extreme Ignitability and Anti-Fouling: These spark plugs offer exceptional ignitability and anti-fouling properties, ensuring reliable performance and longevity.

NGK G-Power Platinum spark plugs are the best single platinum spark plugs at an economical price. G-Power plugs feature a fine wire platinum center electrode and a trapezoidal cut ground electrode that offers increased durability, improved fuel efficiency

Product Features:

• SINGLE PLATINUM TIP: Fine wire 0.6 millimeter platinum tip center electrode ensures improved durability and a consistently stable spark
• PLATINUM ALLOY: G-Power platinum provides exceptional value with increased performance and longer service intervals than factory nickel plugs
• TRAPEZOIDAL CUT GROUND ELECTRODE: Reduces quenching design produces improved ignitability and performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• RECOMMENDED USAGE: Lower cost alternative to double precious metal spark plugs or as an upgrade to OE nickel alloy spark plugs

Autolite has over 100 years of engineering experience and has sold over 11 billion plugs. Designed and engineered in the USA, Autolite Platinum spark plugs provide a center wire platinum firing tip which provides reduced gap erosion, fewer misfires, better performance and increased durability. Consider upgrading to Autolite Double Platinum or Iridium XP spark plugs for increased performance.

Product Features:

• High nickel alloy side electrode maintains precise gap
• Full platinum tip assures virtually no gap erosion for long life
• Necked-down center electrode fires quicker, cleaner with less voltage for easier starts, quicker acceleration and improved fuel economy (as compared to standard plugs)

NGK Iridium IX spark plugs are specifically designed for the performance enthusiast. Iridium IX provides outstanding acceleration, high fuel efficiency and durability. NGK Iridium IX plugs offer extreme ignitability and exceptional anti-fouling. Tapered c

Product Features:

• SINGLE IRIDIUM TIP: Fine wire 0.6 millimeter iridium tip center electrode ensures high durability and a consistently stable spark
• IRIDIUM ALLOY CENTER ELECTRODE: Iridium’s density (6x that of platinum) and extremely high melting point is perfect for modern high efficiency engines
• TAPERED CUT GROUND ELECTRODE: Reduced quenching design produces outstanding ignitability, improved acceleration, fuel efficiency and durability
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• RECOMMENDED USAGE: Modified or high performance applications, or as an upgrade to OE nickel alloy spark plugs

NGK V-Power spark plugs offer reliable performance and improved ignitability over standard nickel plugs. Engineered specifically for OE applications, the special V-cut nickel alloy center electrode and concave ground electrode of NGK’s V-Power spark plug

Product Features:

• ACTUAL OE or EQUIVALENT DESIGN: OEM quality construction nickel alloy center electrode with V-groove provides consistent performance
• RECOMMENDED USAGE: Best for vehicles with OE nickel alloy plugs, not recommended on vehicles with factory precious metal plugs
• NGK’s OE CERAMIC TECHNOLOGY: High grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal

NGK V-Power spark plugs offer reliable performance and improved ignitability over standard nickel plugs. Engineered specifically for OE applications, the special V-cut nickel alloy center electrode and concave ground electrode of NGK’s V-Power spark plug

Product Features:

• ACTUAL OE or EQUIVALENT DESIGN: OEM quality construction nickel alloy center electrode with V-groove provides consistent performance
• RECOMMENDED USAGE: Best for vehicles with OE nickel alloy plugs, not recommended on vehicles with factory precious metal plugs
• NGK’s OE CERAMIC TECHNOLOGY: High grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal

Manufactured to the strictest OE performance, durability and emissions standards.

Product Features:

• Latest OE technology with DENSO’s patented Iridium Alloy (90% Ir) and fine wire center electrode
• Platinum Needle Tip Ground Electrode: Promotes higher spark energy and less heat quenching
• DENSO Patented 360 degree laser welding process: Ensuring exceptional quality bond and structural strength with the Iridium Center Electrode
• Sustained spark performance over 100,000 miles
• Lasts up to three times as long as conventional plugs
• Endures extreme temperatures greater than 4,000 degrees F associated with high-performance ignition and special fuel systems
• Iridium Long Life (SIP)

Durability of an OE style plug combined with Power & Torque of high performance.

Product Features:

• 0.4mm Iridium Center Electrode: World’s Smallest Diameter that maximizes firing potential
• 0.7mm Needle Tip Ground Electrode: Promotes higher spark energy and less heat quenching
• DENSO Patented Optimized Iridium-Rhodium Alloy Formula: Highest concentration of Iridium vs. competitors for greater durability
• DENSO Patented 360 degree laser welding process: Ensuring exceptional quality bond and structural strength with the Iridium Center Electrode
• Durability of an OE style plug combined with Power & Torque of high performance.
• Withstands temperatures greater than 4000┬░ Fahrenheit
• Iridium TT
• Ultimate Endurance and Power: The DENSO Iridium TT Spark Plug features a 0.7mm Iridium Tip, ensuring over 100,000 miles of uncompromised performance.
• Advanced Twin-Tip Technology: Developed from Original Equipment Specification Super Ignition Plug (SIP) design, combining a Fine Wire Iridium Center Electrode with a Needle Tip Platinum Ground Electrode.
• Enhanced Fuel Economy and Lower Emissions: Drive around the Earth over 4 times with improved fuel efficiency and reduced emissions.
• Premium Materials: Features an Iridium Center Electrode Tip and a Flat Seat Type for optimal performance and durability.

Autolite has over 100 years of engineering experience and has sold over 11 billion plugs. Designed and engineered in the USA, Autolite Double Platinum spark plugs feature platinum-to-platinum firing which virtually eliminates gap erosion, reduces misfires and increases durability of the plug. Consider upgrading to Autolite Iridium XP spark plugs for increased performance.

Product Features:

• Works to optimize engine performance for a longer life and improved fuel economy
• OE design
• Full-platinum tips; platinum on both the center and side electrodes to promote reduced gap wear
• Platinum ball welding process provides a consistent point of contact for enhanced adhesion

NGK Iridium IX spark plugs are specifically designed for the performance enthusiast. Iridium IX provides outstanding acceleration, high fuel efficiency and durability. NGK Iridium IX plugs offer extreme ignitability and exceptional anti-fouling. Tapered cut ground electrode provides improved starting, idling and throttle response. The Iridium fine wire center electrode’s durability is six times harder than platinum. Iridium alloy’s extremely high melting point is perfect for today’s engines. For even greater performance consider upgrading to an NGK Ruthenium HX plug.

Product Features:

• SINGLE IRIDIUM TIP: Fine wire 0.6 millimeter iridium tip center electrode ensures high durability and a consistently stable spark
• IRIDIUM ALLOY CENTER ELECTRODE: Iridium’s density (6x that of platinum) and extremely high melting point is perfect for modern high efficiency engines
• TAPERED CUT GROUND ELECTRODE: Reduced quenching design produces outstanding ignitability, improved acceleration, fuel efficiency and durability
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• RECOMMENDED USAGE: Modified or high performance applications, or as an upgrade to OE nickel alloy spark plugs

NGK G-Power Platinum spark plugs are the best single platinum spark plugs at an economical price. G-Power plugs feature a fine wire platinum center electrode and a trapezoidal cut ground electrode that offers increased durability, improved fuel efficiency, lower emissions, faster starts and quicker acceleration over conventional nickel spark plugs. An excellent upgrade for vehicles which used nickel alloy spark plugs originally. For better performance consider upgrading to a NGK Iridium IX plug. For even greater performance consider upgrading to a NGK RUTHENIUM HX plug.

Product Features:

• SINGLE PLATINUM TIP: Fine wire 0.6 millimeter platinum tip center electrode ensures improved durability and a consistently stable spark
• PLATINUM ALLOY: G-Power platinum provides exceptional value with increased performance and longer service intervals than factory nickel plugs
• TRAPEZOIDAL CUT GROUND ELECTRODE: Reduces quenching design produces improved ignitability and performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• RECOMMENDED USAGE: Lower cost alternative to double precious metal spark plugs or as an upgrade to OE nickel alloy spark plugs

NGK Standard spark plugs (in the iconic NGK ‘yellow box’ packaging) are a proven OE cornerstone and technology customers have relied on for decades. Engineered specifically for OE applications, NGK Standard spark plugs provide OE quality nickel alloy reliable performance and design. NGK’s legendary high grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance, while triple gasket sealing prevents combustion gas leakage. Solid 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges. Trivalent metal plating ensures superior anti-corrosion and anti-seizing properties.

Product Features:

• ACTUAL OE or EQUIVALENT DESIGN: OEM quality construction nickel alloy center electrode provides consistent performance
• RECOMMENDED USAGE: Best for vehicles with OE nickel alloy plugs, not recommended on vehicles with factory precious metal plugs
• NGK’s OE CERAMIC TECHNOLOGY: High grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• Triple Gasket Sealing: Prevents combustion gas leakage, ensuring efficient engine performance.

NGK Laser Iridium High Ignitability spark plugs offer the best combination of performance and longevity. Engineered specifically for OE applications, Laser Iridium High Ignitability spark plugs are tested to the highest standards to ensure quality and dur

Product Features:

• ACTUAL OE or EQUIVALENT HIGH IGNITABILITY DESIGN: PSPE tip and iridium alloy center electrode produce the most advanced OE spark plug technology
• IRIDIUM ALLOY CENTER ELECTRODE: Iridium’s density (6x that of platinum) and extremely high melting point is perfect for modern high efficiency engines
• PSPE DESIGN: Projected square platinum electrode shape of the ground electrode provides the best ignitability and service life for high heat engines
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• RECOMMENDED USAGE: Best for vehicles with OE PSPE iridium alloy plugs

NGK Standard spark plugs (in the iconic NGK ‘yellow box’ packaging) are a proven OE cornerstone and technology customers have relied on for decades. Engineered specifically for OE applications, NGK Standard spark plugs provide OE quality nickel alloy reli

Product Features:

• ACTUAL OE or EQUIVALENT DESIGN: OEM quality construction nickel alloy center electrode provides consistent performance
• RECOMMENDED USAGE: Best for vehicles with OE nickel alloy plugs, not recommended on vehicles with factory precious metal plugs
• NGK’s OE CERAMIC TECHNOLOGY: High grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal

Durability of an OE style plug combined with Power & Torque of high performance.

Product Features:

• 0.4mm Iridium Center Electrode: World’s Smallest Diameter that maximizes firing potential
• 0.7mm Needle Tip Ground Electrode: Promotes higher spark energy and less heat quenching
• DENSO Patented Optimized Iridium-Rhodium Alloy Formula: Highest concentration of Iridium vs. competitors for greater durability
• DENSO Patented 360 degree laser welding process: Ensuring exceptional quality bond and structural strength with the Iridium Center Electrode
• Durability of an OE style plug combined with Power & Torque of high performance.
• Withstands temperatures greater than 4000° Fahrenheit
• Iridium TT

NGK Standard spark plugs (in the iconic NGK ‘yellow box’ packaging) are a proven OE cornerstone and technology customers have relied on for decades. Engineered specifically for OE applications, NGK Standard spark plugs provide OE quality nickel alloy reliable performance and design. NGK’s legendary high grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance, while triple gasket sealing prevents combustion gas leakage. Solid 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges. Trivalent metal plating ensures superior anti-corrosion and anti-seizing properties.

Product Features:

• ACTUAL OE or EQUIVALENT DESIGN: OEM quality construction nickel alloy center electrode provides consistent performance
• RECOMMENDED USAGE: Best for vehicles with OE nickel alloy plugs, not recommended on vehicles with factory precious metal plugs
• NGK’s OE CERAMIC TECHNOLOGY: High grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• Triple Gasket Sealing: Prevents combustion gas leakage, ensuring efficient engine performance.

Increased performance with World’s smallest Iridium Center Eletrode (0.4mm).

Product Features:

• World’s smallest Iridium Center Electrode (0.4mm) for improved spark for maximum combustion
• Patented 360-degree laser welding assembly process
• U-groove and taper cut ground electrode to maximize flame propagation.
• Withstands temperatures greater than 4000° Fahrenheit
• Burnished nickel plating for high temperature endurance and superior corrosion resistance
• Wide range of part numbers for thousands of applications, including classic and collector cars
• Iridium Power

Increased performance with World’s smallest Iridium Center Eletrode (0.4mm).

Product Features:

• World’s smallest Iridium Center Electrode (0.4mm) for improved spark for maximum combustion
• Patented 360-degree laser welding assembly process
• U-groove and taper cut ground electrode to maximize flame propagation.
• Withstands temperatures greater than 4000┬░ Fahrenheit
• Burnished nickel plating for high temperature endurance and superior corrosion resistance
• Wide range of part numbers for thousands of applications, including classic and collector cars
• Iridium Power
• Superior Performance: Engineered for maximum performance under extreme conditions, this spark plug delivers more horsepower, faster and easier starts, and fewer misfires under heavy loads.
• Enhanced Fuel Efficiency: Thanks to its advanced design and patented technology, the Iridium Power plug improves fuel efficiency, making it an economical choice for your vehicle.
• Low Voltage Requirement: The DENSO Iridium Power spark plug requires 5,000 volts less to fire compared to conventional spark plugs, ensuring reliable ignition with lower energy consumption.
• Durable Iridium Material: Constructed with a durable iridium center electrode tip and a flat seat type, this spark plug offers long-lasting performance and reliability.

Champion® Double Platinum Power¿ spark plugs deliver more powerful performance. Featuring exclusive Heat-Active¿ alloy, platinum fine wire center electrode and platinum pad ground electrode provide maximum life and sharper spark focus.

Product Features:

• Double Platinum Power – Premium Spark Plug. More Powerful Performance.
• Platinum center and ground electrode for greater wear resistance
• Maintains stable operating temperature under all engine loads
• Fine-wire center electrode for greater ignitability
• V-trimmed ground electrode promotes sharper spark focus
• Heat-Active┐ alloy allows electrodes to reach optimal temperature

NGK Ruthenium HX High Ignitability spark plugs are the best in class plug for todays modern vehicles. Patented Ruthenium technology offers the most advance tip technology and delivers the highest performance and life expectancy. Created from advanced OE t

Product Features:

• HIGH IGNITABILITY DOUBLE FINE ELECTRODE DESIGN: Combines 0.6 millimeter ruthenium center with opposed fine wire platinum ground electrode
• RUTHENIUM ALLOY CENTER ELECTRODE: NGK’s patented ruthenium technology produces maximum performance, ignitability & durability at high temperatures
• PLATINUM PIN TYPE GROUND ELECTRODE: Provides more complete fuel burn, quicker throttle response, smoother idle and better cold starts
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• RECOMMENDED USAGE: Modern vehicles using OE DFE type spark plugs or for those seeking an aftermarket plug with the latest OE technology

NGK Laser Iridium High Ignitability spark plugs offer the best combination of performance and longevity. Engineered specifically for OE applications, Laser Iridium High Ignitability spark plugs are tested to the highest standards to ensure quality and durability. Iridium tipped center electrode provides durability six times harder than platinum. NGKs high grade pure alumina ceramic and 98 percent pure copper core prevents the spark plug from overheating while providing reliable starts. Laser Iridium High Ignitability spark plugs feature raised platinum pad or platinum fine wire tip on the ground electrode for even wear in distributorless ignition systems and improved spark performance.

Product Features:

• ACTUAL OE or EQUIVALENT HIGH IGNITABILITY DESIGN: SPE tip & iridium alloy center electrode produce the most advanced OE spark plug technology
• IRIDIUM ALLOY CENTER ELECTRODE: Iridium’s density (6x that of platinum) and extremely high melting point is perfect for modern high efficiency engines
• SPE DESIGN: Square platinum electrode shape of the ground electrode provides the best ignitability and service life for high heat engines
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal
• RECOMMENDED USAGE: Best for vehicles with OE SPE iridium alloy plugs
• High Grade Pure Alumina Ceramic: Prevents overheating and ensures reliable starts, enhancing overall engine performance.
• Raised Platinum Pad or Platinum Fine Wire Tip: Ensures even wear in distributorless ignition systems, improving spark performance and longevity.
• OE Series Design: Engineered specifically for original equipment applications, tested to the highest standards for quality and durability.

Manufactured to the strictest OE performance, durability and emissions standards.

Product Features:

• Latest OE technology with DENSO’s patented Iridium Alloy (90% Ir) and fine wire center electrode
• Platinum Needle Tip Ground Electrode: Promotes higher spark energy and less heat quenching
• DENSO Patented 360 degree laser welding process: Ensuring exceptional quality bond and structural strength with the Iridium Center Electrode
• Sustained spark performance over 100,000 miles
• Lasts up to three times as long as conventional plugs
• Endures extreme temperatures greater than 4,000 degrees F associated with high-performance ignition and special fuel systems
• Iridium Long Life (SIP)
• Enhanced Engine Efficiency: Enjoy more horsepower, faster and easier starts, and fewer misfires under heavy loads, ensuring better fuel conservation at all times.

NGK Standard spark plugs (in the iconic NGK ‘yellow box’ packaging) are a proven OE cornerstone and technology customers have relied on for decades. Engineered specifically for OE applications, NGK Standard spark plugs provide OE quality nickel alloy reliable performance and design. NGK’s legendary high grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance, while triple gasket sealing prevents combustion gas leakage. Solid 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges. Trivalent metal plating ensures superior anti-corrosion and anti-seizing properties.

Product Features:

• ACTUAL OE or EQUIVALENT DESIGN: OEM quality construction nickel alloy center electrode provides consistent performance
• RECOMMENDED USAGE: Best for vehicles with OE nickel alloy plugs, not recommended on vehicles with factory precious metal plugs
• NGK’s OE CERAMIC TECHNOLOGY: High grade alumina silicate ceramic creates a stronger insulator for optimal dielectric performance
• SOLID COPPER CORE: 98% pure copper core offers superior heat dissipation, conductivity and ultra wide heat ranges
• COLD-ROLLED THREADS: Prevents cross-threading and damage to cylinder heads
• TRIVALENT METAL PLATING: Delivers superior anti-corrosion and anti-seizing properties, ensuring ease of installation and removal

The ground electrode is cut-back from the center electrode to provide a gap. The face of the ground electrode is concave to provide a constant gap to the center electrode. This plug is designed use in all aftermarket cylinder heads used in different types of racing venues including oval and road racing.

Product Features:

• Opens spark face for better ignitability of flame kernel
• Retains less heat, transfers heat to shell faster – reduces risk of pre-ignition
• Dyno testing has shown proven power gains
• Cut-back ground electrode evolved from practice of grinding back the side electrode