Powered by Lumenok. Engineered for modern, high performance crossbows. Capture Nock designed for safety and accuracy. Exclusive, PATENTED design. Battery Life of over 40 hour. Standard Replaceable Battery (BR 425). Lights when the Arrow is shot. Switch Off Easily by Pressing on the Nock. Fits the Following Crossbow Arrow Brands: Parker Hunter Arrows (2013) and others with inside diameters of 0.300”. 28 Grains.