its the same as a 727 I believe its a 5/16 ball but I am not at work so not positive but you may find one at a hardware store

70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake

best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4