From the thread about replacing the grip locator pin it was mentioned about thread gages;
Brownells has them for both standard and metric, $15-$20 Standard goes from 1-48 to 5/16-32
https://www.brownells.com/gunsmith-tools-supplies/measuring-tools/thread-pitch-gauges/screw-chek-r-prod775.aspx
Comes in real handy when checking screw sizes from older guns that didn't use what now are common threads. Also it is hard enough to clean up slightly battered threads, but don't use it to try to fix really beat up, stripped threads, get your dies or thread restorer out for that work (or buy new ones from a major industrial parts place like McMaster-Carr).
Brownells has them for both standard and metric, $15-$20 Standard goes from 1-48 to 5/16-32
https://www.brownells.com/gunsmith-tools-supplies/measuring-tools/thread-pitch-gauges/screw-chek-r-prod775.aspx
Comes in real handy when checking screw sizes from older guns that didn't use what now are common threads. Also it is hard enough to clean up slightly battered threads, but don't use it to try to fix really beat up, stripped threads, get your dies or thread restorer out for that work (or buy new ones from a major industrial parts place like McMaster-Carr).