Compatibility This tool is specifically designed for Isuzu 6.6L Duramax 2001-Later GMT800, 2500HD, 3500 with 6.6 liter Duramax diesel engines. Function This tool is used to install the seal to correct depth and position. The crankshaft rear seal will fit perfectly to the engine block and crankshaft. It is of vital importance to keep both the inner and outer seal bodies fit well and in good alignment, otherwise it may cause leakage. Easy Installation .