Altra Arrows™ Centrum 166 Premier line sets the mark for quality with industry leading straightness of .001”. Using state-of-the-art measuring equipment to verify arrow shaft and component straightness, along with Altra’s weight-matching process ensures you are getting the most consistent arrows available. Construction: Proprietary blend of high-modulus carbon ID: .164" Straightness: .001" Weight Tolerance: +\- 1 gr Weight: 250 spine (11.5 gpi), 300 spine (10.5 gpi), 350 spine (9.4 gpi), 400 spine (8.5 gpi) Quantity: 12-pk Included Components: A.R.C.O.S. Insert/Outsert System and nocks