The SRS features two different sizes. The Tactical, and the Hunter. The Hunter is pocketed out to reduce weight. These all come with 5/16-24 threads and taper to .400″. We have three groove options, straight groove, eight spiral, and five spiral. (Spiral is measured in spirals per inch, so 8 is a tighter spiral) – Tactical : .860″ OD, 1.25″ OAL, 1.25 oz. – Hunter: .760″ OD, 1.125″ OAL, .55 oz.