Smith Enterprise is now offering the upgraded G6A4 Vortex with Arc Helix. The Arc Helix has been designed to even further facilitate the installation/removal of the Smith Enterprise Windtalker sound suppressor, coupled with a shallower pitch and grooves to reduce surface contact and carbon buildup. Through test and evaluation they have also found that the Arc Helix has proven itself to retain better accuracy as the round leaves the suppressor. Heat treated same as all other Vortexes. 1/2 x 28 I.D. thread. Mfg: Smith Enterprise