UP100&reg; 6PCS Automatically Led Arrow Nocks for Aluminum Crossbow Arrows ID .297-.302" Hunting High-Visibility LED Color Blue Bowstring activated on-off switch Breakthrough design. 30 grains total weight Half moon shape nocks Fits for crossbow bolt size 0.297"-0.302"(7.6mm) ID Can be lighted about 48 hours. Work for: Aluminum arrow shafts & carbon arrow shafts & glassfiber arrow shafts After the battery is weak. Please do not throw away, After a period of time, It can be a few hours again work, Until power is completely off.