Necessary for mounting Cold Spring Front Rack or Ultimate LowRider Front Rack to suspension forks that lack brake posts. To determine the size Band Clamps you need, you will need to measure the diameter of your seat stays (rear racks) or forks (front racks) where you will be mounting the extenders of your OMM rack. To determine the diameter, take a piece of string and wrap it around the seat stay or fork. Measure the length of the string and divide it by 3.14 to get the diameter. You can also hold a ruler against the tube and eyeball the diameter. Three sizes to choose from.