alisske Posted March 1, 2009 Share Posted March 1, 2009 I purchased a set of Meprolight tritium sights for my M4. The OEM windage screw on rear sight does not fit into the new meprolight rear sight. (this is the screw the gives the windage adjustment) The OEM screw is tight and I am afraidto strip it. I wanted to tap the meprolight sight to clean up the threads on it. Does anybody know the tap size? I have been struggling with it for a month or so. Thanks Anthony Quote Link to comment Share on other sites More sharing options...
tucker301 Posted March 1, 2009 Share Posted March 1, 2009 Don't know. If you don't get an answer here, simply remove the screw and take it to a machinist and ask him to gauge it for you. Or for just a few dollars.... http://www.boltdepot.com/Thread-Gauges.aspx Quote Link to comment Share on other sites More sharing options...
Guest cleefurd Posted March 1, 2009 Share Posted March 1, 2009 (edited) I just checked mine, it is definitely NOT metric, but a 6-48 tap will almost go through my OEM one by hand. The 6-48 major dia is .137" according to unified thread call-out, and your screw should mic' out at around .135" with exactly 48TPI. Long story short, run a 6-48 tap through it with a good cutting fluid and stop as SOON as the tap begins to turn freely, back it out and I bet your new sight will work perfectly. I used a comparator and thread leafs to determine that the 48TPI is EXACTLY what you have OEM. Edited March 1, 2009 by cleefurd Quote Link to comment Share on other sites More sharing options...
alisske Posted March 2, 2009 Author Share Posted March 2, 2009 Cleeford, I guess it goes with out saying, but I will say it anyway... THANK YOU! I am ordering the tap today and will follow your recomendations. I have been looking at those sights for 2 months now. (After visiting 7 different hardware stores with no luck) Be well Quote Link to comment Share on other sites More sharing options...
Guest cleefurd Posted March 3, 2009 Share Posted March 3, 2009 When you order try and find an "H1" limit tap, which would be near the low side of the limit thread standard (smaller). Of course an "H2" or "H3" would work as well, since the difference is actually miniscule, but as I stated all 3 of my windage screws for that sight were .135" major external dia, so the tapped holes they would require favor the "H1" class 6-48 taps. The advantage in doing this is slightly tighter fit for a more precision fit. I enjoy finding and providing helpful info in return, more often than not simply passing on what was shared with me too. Good luck with your new sight. Quote Link to comment Share on other sites More sharing options...
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