The Mikmar Bits come in threesizes: 5.25 inch, 5.5 inch, and 6.25 inch. Their unique design makes it unnecessary to break down the width of the mouthpiece into quarter inch increments smaller than 5.25 inch, (like a snaffle for example). The 5.25 inch bits fit anywhere between medium size ponies, up to large Warmbloods. We do not recommend the 5.25 inch for Small Ponies (Shetland type) or Medium to Large Draft Horses. The 5.5 inch is ideal for very large mouthed warmbloods, but most warmbloods fit in the 5.25 inch. The 6.25 inch mouthpiece is for any size Draft Horse. The design of the mouthpiece and the shanks makes it possible for the bit to work on different size mouths, without any discomfort to the horse or loss of bit effectiveness.