This is from Howell's book. He advises deducting .006 for measurement over varnish. 17/64 ferrule in. Butt Tip o .330 .258 5 .330 .248 10 .330 .225 15 .320 .210 20 .314 .202 25 .296 .182 30 .288 .176 35 .284 .144 40 .270 .122 45 .266 .102 50 .264 .086 52 .262 .084 Hope this helps. Brian Justiss