Ok which Savage barrel are we talking about here?

Most of the heavier barrels from Savage are either 1/2"-28-RH for rimfire stuff and .224 cal stuff and 5/8"-24-RH for anything bigger.

The factory barrels setup for the Adjustable Brake that turns on/off are threaded 9/16"-28-RH which is a Savage proprietary thread.

Frank, if you are wondering what your 30-06 barrel (that I sold you) is, I had it threaded 5/8"-24-RH.

EDIT: just saw you said this is for a 308. If its a heavy varmint/bull barrel then it should be 5/8"-24-RH and if a Sporter or Magnum taper barrel with the on/off brake then 9/16"-28-RH.