I can’t seem to find the size thread protector I need, its an older Midway 10/22 bbl, calipers show the OD of the threads approx .750", and .650" long. It’s bigger than a 5/8 so I have no clue. In the pic you can see the threaded portion is almost as big as the .920 bbl’s OD. Thoughts?
Well, since .750 is 3/4’’ I’d say it’s 3/4’'… wait is this a trick question?
Since the OD on the barrel is .920", the next available thread size is 7/8" (.8750") with a pitch of -9,-14, or-20 threads per inch. The next step down is 1-3/16" (0.8125") with a pitch of -20 threads per inch. And finally if the major diameter of the thread, as you measured it is indeed 3/4" (0.7500"), then you’ll have to determine if the pitch is -10, -16, or -20 threads per inch to find the appropriate thread protector for your needs.
For your future reference, here’s a drill and tap chart to help you out:
http://www.physics.ncsu.edu/pearl/Tap_Drill_Chart.html
They definitely made it difficult enough, eh?