Product Descriptions Application It used with diesel compression tester TU-15. Insert the M10-1.25 threaded adapter quick disconnect screws into the glow plug hole in the head of the engine. Fits for 6.6L Diesel Duramax engines, 2005 to present. Function This test adapter used with diesel compression tester TU-15, mainly used to measure the maximum pressure generated in the compression stroke of the diesel engine cylinder. Specially designed to check the compression pressure of gas in the cylinder. Material .