100% brand new and high quality Introductions: Inner diameter is 27.2mm/1.07inch, 3 type of outer diameter to choose Use this seatpost sleeve adapter ring, you can use 30.4/30.8/31.6mm seatpost on your 27.2mm bike seatpost Can be converted to 27.2 seatpost diameter of 30.4 or 30.8 or 31.6 diameter, just this little accessories can save money to buy a seat tube. Suit for MTB bike, mountain bike, road bike etc Please check your bike frame seat tube outside diameter. measure the inside diameter of your old clamp.Or measure the outside diameter of your seat tube (on your bike frame). then make a right choice Specification: Material: Aluminum alloy Inner diameter: 27.2mm/1.07inch Outer diameter: 30.4mm/1.20inch; 30.8mm/1.21inch; 31.6mm/1.24inch... .