Thomson oversize rail clampsaddles with carbon rails tend to be oval and larger 7 x 9mm and 7 x 10mm being the common over sized rail dimension there are also downhill and bmx saddles with round metal rails at 8 and 9mm so if you have rails larger than 7mm do you need this new clampset maybe maybe not thomsons standard rail clamps can accommodate rails up to 7 x 10mm but riders using their setback post with over sized rails may have issues getting the saddle nose down if this is you the