[rotorwrench]

The gears produced after mid 1951 all come nearly to a point on the teeth and are referred to as diamond teeth due to that shape. The early ones all have a noticeably more rectangular shaped blunt tip and they don't come to a point at all. I've never tried to fit any diamond tooth types outside of a set. The first/reverse gear is nearly the same for all the different sets that have the helical internal splines with the diamond tooth type being the exception since it has 28 gear teeth instead of 29. The 21C-7100 gear was used clear up to early 1951 for the Mercury cars. The 8M-7113 cluster was a replacement part for all the 39 & later standard "car type" transmissions with the late type synchro. Now days they reproduce the original 68-7113-A as a replacement cluster gear but it takes the early type four notch rear thrust washer instead of the oblong type of the later clusters. It uses the caged roller set like most of the early ones.