Compact design works great in tight spots. Vise opens to 2-1/8". Relieve clamp spring pressure in very tight spots. Tool can be left on during service. Tighten knurled knob by hand or with a 1/4" drive ratchet. Not recommended for 3/8" steel Tool is used to relieve clamp spring pressure in very tight spots. Vise can be left on, with the clamp compressed, during service. Ramp on jaws guides tab of clamp into correct position and traps it in the slot for safety. Tighten knurled knob by hand or with a 1/4" drive ratchet.