500 ratio takeoff drive adaptor kit for installing engine synchronizers and mechanical cable or generator driven tachometers on Detroit marine diesel engines. Will also work on V8 gasoline engines. Note that the standard Glendinning drive kit that’s used with Chrysler and Chevrolet marine gasoline engine uses a slightly shorter takeoff cable: A 3 and 3/4″ takeoff cable instead of a 4″ takeoff cable. Complete kit with 4 inch takeoff cable, locking nut and slotted crankshaft pulley bolt insert. Both kits are configured as non-reversing (Output shaft rotates in the same direction as the input shaft). Both drives can be reversed by unscrewing the end cap and the output shaft threaded sleeve, taking the output shaft out and flipping it around 180 degrees, then swapping the end cap and the output shaft threaded sleeve out with each other (For marine propulsion systems with one clockwise rotating and one counter clockwise rotating engine). Never used or installed drives, not return items. 7/8-18 thread pattern on the male threaded sleeves. 188 diameter slotted holes in the crankshaft pulley bolt insert. 187 diameter tanged tips on both ends of the takeoff cable. 188 diameter slotted hole in the output shaft. The adapters have been confirmed to have a. 500 ratio (Output shafts rotate exactly 5 times when the input shaft is rotated 10 times). I won’t give the discount if you ask me after you pay for X, or if you are reading this after you bought two different items that don’t include this one.