Nano-XRZ featuring Tri-Spine technology which combines stiffer ends with a softer spine center for ultimate accuracy out of a compound bow. Like the Nano-SST for recurve archers the Nano-XRZ is constructed from 30-Ton carbon that ensures faster recovery out of the bow and superior down range performance. Straightness: .0025â?쳌, Weight Tolerance: 2 grains. Available sizes: 350 (9.9 gpi), 400 (9.0 gpi), 500 (7.8 gpi), 600 (7.0 gpi), 700 (6.3 gpi), 800 (5.7 gpi).