The tracks refer to the shoes used for each type. The most common ones are:
T48 -- rubber "v" shaped chevron (thick) T49 -- three bar cleat (e.g. three steel bars that stick up, two on one side, one on the other) T51 -- "irreversible" (e.g. thicker on one side than the other) smooth rubber pads T54E2 -- steel tracks with two openings on the sides and a flat "u" shaped cleat (thin) in the center.
The M10 kit comes with T51 tracks. Most of the USMC tanks seem to use whatever came on the tanks from the factory.
Cookie Sewell