ODIER Bike Bicycle Quick Release SeatPost Clamp 34.9mm 31.8mm MTB Bike Road Bike Casual Bike Seatpost Clamp Aluminum / Carbon fiber Quick Release Bike Seat Clamp. Weight: 38g Material: 7005 Aluminum Alloy. Diameter:31.8mm Easy to Use. High Quality (ISO 9001,14001) PLEASE MEASURE YOUR SEATPOST SIZE: The "31.8", "34.9" refer to the seat post tube diameter not the seat post diameter!