Its from an older 10 bolt, the ones used in 2nd gen f-bodys and olders nova's etc.. 3GM 3988577 11 41 7 78 is stamped on it.

 

Sounds like a 8½" 10-bolt 3.73 (41/11 = 3.73), stock Z28 gear among others

pretty useless unless you have the pinion that goes with it

 

yep have the pinion gear as well, its the origonal gear set from my 73 nova ss which should be 373's but i wanted to double check.. doubt i'll be using it any time soon though.. i was just cleaning the carrier up and i noticed that where one of the locks bolts goes through the pinion shaft it looks as if who ever removed it had a tough time getting it out as it looks like the bolt may have been ceased and broke away the bottom part where the treads should be for the bolt to go into.. would it be possible to tap it below there and use a longer bolt to hold the pinion shaft in or should i start looking for a new carrier?