GrovTec GTHM246, Thread Protector, Black Oxide Finish, Black, 1/2X28 Threaded, .625 Diameter, Fits Pencil Barrels GTHM246 GrovTec's Thread Protector's are the perfect choice for protecting your threaded barrel. Available in popular thread pitches and exterior diameters" GrovTec's Thread Protectors will give your barrel a lifetime of protection and keep your threads in perfect working condition.