GEMTECH Thread Protectors will... protect your threads. We stock most all standard sizes:
1/2x28 (0.41" long): For rimfire rifle and pistol, and 9mm handgun applications.
M13.5x1mm Left Hand: For Sig P226, HK USP9SD, and Smith & Wesson M&P9 SpecOp.
0.578-28: For 1911, Glock 21 (aftermarket), Sig P220 Combat, and FN FNP.
M16x1mm Left Hand:: For the HK USP Tactical, USP-CT, HK45, HK45c and Factory Glock 21.
M16x1mm Right Hand: For the HK Mark 23 SOCOM.
5/8-24 (0.61" long): For use with any rifle that is threaded 5/8-24x.61"
MP5 Thread Protectors: These thread protectors bring "Navy" type MP5 barrels up to spec for use with 3-lug devices, and thus are smooth, not knurled.
1/2-28: Aftermarket MP5-N conversions
1/2-32: Factory HK MP5-N barrels
M14x0.75mm: factory HK MP5/40 and MP5/10 barrels
These protectors will tighten down easily onto most any appropriately-threaded pistol or rifle barrel, keeping fine threads from being damaged from bumping around gun cases, or when you're not using your suppressor.