The NiteRider Standard and Aero Seat Post Straps provide options for a proper and correct fitment onto standard and aero seat posts. Installation is easy with the loop around and hook design. Fitment for: Standard– 27.2mm in diameter seat post Aero– 30.9 or 31.6mm diameter seat post Standard Strap Length, 3.625″ length with comfortable stretch to 5.5″ length Aero Strap Length , 5.5″ length with comfortable stretch to 9″ length For larger/oversized seat post fitment, see NiteRider Accessory SKU 5099 – Oversized Strap. SYSTEM COMPATIBILITY Sentry Aero 260 Daylight Visible Tail Light Bullet 200 Daylight Visible Tail Light ACCESSORY INCLUDES (1) Standard Seat Post Strap (1) Aero Seat Post Strap 5.5″ length with a comfortable stretch up to 9″