I ordered a 1.225 aluminum bushing, and the lead shims brownells sells for their vise for this purpose - they are .045 thick. This with some rosin should get me nice and snug. My barrel is 1.2 exact - another forum reports a3 barrels are 1.195 - I suppose the extra .005 could be the park finish. Brownells has a 1.2" steel bushing, but being my first time using this vise, I didn't want to chance it slipping with no room for a shim. Others have advised and succeed using an undersized (1.15 or 1.175) aluminum bushing for its malleability.