JMP piston stop tool for all two-stroke With wire plug M12 x 1.25. The engine is blocked by the piston, to loosen the nut on the engine. Please be very careful use. Slowly rotate the piston against the stop, then loosen the nut forcefully while increasing slowly. We take no responsibility for broken piston heads! This tool can be seen as a last resort when all other Vario locking tools do not apply and no impact wrench available.