J-46386 Mercedes Benz MBE900 Compression Test adapter. To use the J46386 first make sure your engine is up to 158-203 degrees. Turn off engine and remove nozzle holder from head. Insert compression test adapter J-46386 and secure with hold down and bolt. O-ring must point towards test adapter. Turn hold down clamp until button in base of clamp is aligned with locating element in end cover. Disconnect electronics to prevent engine starting. Crank engine at least 8 revolutions per cylinder. As always refer to your engine manual for complete procedure.