Front sway bars are held to the body by two "U" shaped brackets with this mount inside it... size is 1& 1/8  or 28mm front for many of the standard 2nd generation Firebirds & Camaro's, many of the big car series like Impala/ Bonneville/ GM etc.

NOTE THAT SOME MODELS USED A BIGGER 1 1/4" / 32 mm front bar also.

This is the 1 & 1/8" inch main big bar type, this is typical of what was used from early 70's to later 70's in Firebird & Formula & Standard Camaro.