Bought a 12 bolt posi carrier that looks like new, plates and gears both, but it has only 28 splines for the axles. Pinion gear shaft measures the same as car not truck diameter. Is it an old style "O" for early vehicles or what
Couldn't use it, would like to be able to ID it so I can sell it to someone who CAN use it. Any help greatly appreciated.

 

Here's also a pic of the casting numbers if that'll help...

 

It is a pontiac Olds Buick Chevy Caddy 10 bolt cover / 12 bolt guts posi. 17-2 holding like 2.73-3.08 gears or less.

there is a 17-1 which holds 2.28-2.56
and a 17-3 which holds 3.23-3.42 gears

Ring gear bolts are 7/16 left hand thread and will not interchange with the old 12 bolt chevy rears.

There are 2 versions of these units 28 and 31 both c-clip

These were used in the 1970's ish FULL size cars 31 being used in the earlier years and the 28 in the lower power NON large cubic inch motors of the late 70's.

So any full size car (Cadillac, Electra, Bonneville, Lesabre, olds 88, olds 98 etc.) from 75-80 with a tempest looking rear 10 bolt cover (NOT the same, just looks the same)