Two thread pitches cover almost every AR-15 and AR-10 barrel you will encounter: 1/2x28 and 5/8x24. Picking the wrong one is the most common reason a muzzle device arrives and will not thread on. Most guides stop at "check your barrel." This one explains why the two pitches exist, which calibers use which, and what actually interchanges once you know your thread. Why Two Pitc …
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