When you need the absolute best from your training data the accuracy and reliability of the RED XPLR AXS Power Meter is the way to go. The spider design uses a proprietary thread-on chainring mount system which allows us to reduce weight and increase stiffness without compromising the ability to swap rings. A dual sided power measurement system it's accurate to +/-1.5% even as weather conditions change and boasts unbeatable battery life.Thread Mount design is light stiff and accurate and fits RED XPLR Thread Mount chainrings 38t-46t (Chainrings sold separately)Dual sided power measurement system it's accurate to +/-1.5% even as weather conditions change and boasts unbeatable battery life (User replaceable CR2032 battery with 200-hour battery life)Bluetooth low energy technology and ANT+ wireless data transferMagicZero automatically checks and recalibrates your power meter as you rideNo cadence magnet required10K Temperature Compensation and Waterproof (IPX7 waterproof to 1 meter for 30 minutes)AXS(TM) enabled for easy monitoring and firmware updatesIncludes 8 bolts and thread back up pin for chainring