The 8 1/4 thread

Jeep 8.25 will work if they are 1995 and older and most jeep rears are 3.07 ratio if out of a 6 cylinder (4.0) manual transmission or 3.55 ratio 6 cylinder with auto transmission. The 4cylinder jeeps had 4.10 with manual transmission and autos have 4.56 (very rare)
And some came with 3.73 with a economy package. This info is for Cherokee jeeps only. 8.25 didn't come in grand cherokees

Also Docotor Diff sells the larger axles shafts with 29 splines instead of the 27 splines in A body length so you can use the later jeep Trac Loc's. The axles he sells are better material and much larger shaft than stock ones.