"Thanks to high-grade carbon shafts, premium components, and sophisticated manufacturing processes, Altra Arrows Centrum Limited 166 Arrows deliver top-flight accuracy and superior consistency. Sophisticated construction uses a proprietary blend of high-modulus carbon that features NO SPINE Technology for improved tunability and reliable arrow-to arrow uniformity. State-of-the-art measuring equipment verifies arrow shaft and component straightness up to .003"" for unmatched precision. Centrum Limited 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-grade carbon shafts and premium components Top-flight accuracy with superior consistency Proprietary blend of high-modulus carbon NO SPINE Technology for improved tunability Straightness .003"""