A-B123139GS-AI KEY-SQUAREOne New Aftermarket Replacement Square Key Fits Briggs and Stratton (Fits Briggs & Fits Stratton) Small Engines This square key is a small but essential drivetrain component used on Fits Briggs and Stratton engines. It seats into the keyway on the crankshaft or pump drive shaft, locking rotating components in precise alignment and preventing slippage during operation. Commonly used on pressure washers, lawn mowers, and other outdoor power equipment