Ultra compact seat bag is hidden under that saddle with hook and loop fastening strap to carry inner tube and tire levers for a safe and secure ride. Built-in anti-slip fabric provides mounting security Features a built in anti slip strap to store extra gear on the outside of the pack Topeak&';s Rail Wing system securely attaches the bag while also allowing for access when attached Capacity: 12 cu in (x small); 18 cu in (small); 30 cu in (medium) Attachment: Hook and loop fastening strap (Rail Wing System) Compatibility: XS - Up to 700 x 28c inner tube / 2 tire levers; S - Up to 700 x 50c inner tube / 2 tire levers; M - Up to 29" x 1.75"-2.5" inner tube / 2 tire levers / mini tool or CO2 cartridge Dimensions: 4.1" x 2.8" x 1.1" (x small); 4.1" x 2.8" x 2.2" (small); 5.3" x 3" x 2.2" (medium) Weight: 42g. (x small); 47g. (small); 54g. (medium) Color: black