All are different, but as mentioned 5/8" ( .625) is pretty common for 5/8" tenons.
Smaller diameter= shorter thread engagement, larger= longer...
A small 9/16" Harrell's brake I use a lot is only a . 500 tenon.
As you noted, also dependent on brake design; JP has a recommended depth for a cup/chamber behind the first baffle of their Recoil Eliminator.