Product Description: ??Perfect Fit?? Diesel Compression Test Adapt Adapter uses with STAR Diesel Compression Tester TU-15. Compatible with GM: Duramax 6.6L Turbo Diesel (2005-present). Also works on a Duramax LML engine. ??Perfect Design?? M10-1.25 thread adapter with quick disconnect screws into the head of the engine in the glow plug hole. Manufactured to specific thread tolerance standards. .