GM Style 10 bolt gasket - with scolloped sides as shown... scollopes mean the sides between say 8 & 10 oclock or  2 & 4.. curve IN..

     Mainly used on GM A & B & some G bodies ( early 70's Impala etc..plus GTO, Chevelle, Cutlass).

LOOK AT HOW THE GASKET SCOLLOPS IN ON THE SIDE OR not.. on yours to know the difference in the 10 bolt gaskets.

This one often also referred to as a "12 bolt" diff internally but has the 10 bolt inspection plate.... so do match it up exactly 

If unsure.... check pattern as shown before ordering.