Specifications:Material: 6601 Aluminum alloy, light weight and durable.Matte Finish: Polished anodized finish,exquisite workmanship and never rust.Diamter: 25.4 mm 27.2 mm 28.6 mm 31.6 mm.Length: 350 mm.Wall Thickness: 3 mm.Color: Black / Red / Blue.Weight: About 170 g.With the general specification of the dimensions of the clamp,it fits most of the saddles (the four sizes commonly used for you).How to measure and choose the diameter that you need:Check the diameter mark on your old seat post, normally there's a size mark on your old seat post. For example, if there's a mark " ? 25.4"on your old seat post, then you can buy a new 25.4mm seat post.If you have a vernier caliper, measure your old seatpost diameter, or measure the inner diameter of the seatpost hole, then buy a similar size new seat post. For example, if the measurement is about 27.1mm, then select a 27.2mm seat post will do.NOTE:This is for a seat post only, the saddle clamp is NOT included. Please buy a saddle clamp separately or remove one from old saddle.Please do measure and confirm the exact post diameter that you need for your bike. Otherwise you may find it too small or too large for your bike frame seat post hole, then you'll have to spend more time to return it. Thank you for your support.There is a safety line mark on the seat post. Please insert at least above the minimum safety line when installing the new seat post.