"Expect the highest level of precision from Altra Arrows Centrum Premier 166 Arrows. Sophisticated construction uses a proprietary blend of high-modulus carbon that features NO SPINE Technology for improved tunability and reliable consistency. State-of-the-art measuring equipment verifies arrow shaft and component straightness up to .001"" for maximum precision. Centrum Premier 166 arrows include A.R.C.O.S. Insert/Outsert System and nocks. Note: Manufacturer highly recommends using a foam-style arrow target when shooting A.R.C.O.S.-equipped arrows. Weight Tolerance: 1 grain. High-modulus carbon shafts and premium components Precision accuracy with superior consistency NO SPINE Technology for improved tunability Straightness .001"""