Altra 204 Half Outsert 350-400 Spine Fits Altra Arrows 204 Shafts;Machined from 7075-T6 aluminum for unmatched durability;Secure insert depth: 1.00 inch;Tapered design for perfect fitment;Compatible with standard 5/16" field points;Included with all 204 Novum arrows;Compatible with 204 Centrum Limited and Premier arrows;Achieves a lighter total arrow weight compared to the A.R.C.O.S. system;Comes in 12 pk QTY;Available in two sizes: 250-300 Spine & 350-400 Spine;25 Grain Total Weight;Accepts micro FMS insert weights