Stanley 85-721 3/8-Inch Drive 6-Point Professional Grade Spark Plug Socket Set, 3-Piece Stanley Sockets feature our Max-Drive design, a unique radius corner design which provides 15-Percent more torque, making it easy to tighten fasteners and simplifies the turning of rounded corners Helps reduce fastener wear without contact on outer 5-Percent of fastener, so fasteners last longer Helps reduce slippage on frozen or rusted fasteners Limited Lifetime Warranty