Carbon Express Nano-Pro, Carbon Target Arrow Shaft (Designed for FITA, NAA and NFAA), Size 550, 12-Pack Designed for fit a and NCAA long-distance field shooting Light and Strong with 46-ton carbon construction Straightness tolerance of +-.0015 inch Weight tolerance of +-1 gr Advanced technology, extreme accuracy Straightness: +/- 0.0015" Weight tolerance: +/- 1.0 grains Spine selection tolerance: +/- 0.002" Item specifications: 550-Size, 7.1-GPI, 0.550-inch Spine and 0.193-inch Diameter