It is important to choose the correct size of SMB for your horse. The circumference measurement of the boot is critical, because the boot must fit around the horse’s leg and overlap 1/2″ to 1.5″ to be effective. As a general rule, horses will use the same size on both the front and hind legs. However, in such instances where a horse may have pronounced size differences in the fetlocks, the horse may wear a smaller size on the front than on the hind, or vice-versa.