Carbon Express 50122 Nano-Pro Pin Nock Adapter, Size #1 (Fits Nano-Pro 350-550 and Nano-Pro X-Treme 400-500), 12-Pack Fits Nano-Pro 350-550 and Nano-Pro X-Treme 400-500 spines Takes all standard pin nocks Constructed from aircraft grade 7075-T6 aluminum Weighs 7.1 Grains 12 per pack