The American Miniature Horse Registration (AMHR) is a sister organisation of the American Shetland Pony Club (ASPC) and is the oldest miniature horse registry in the USA. The AMHR divides miniature horses into two categories: horses up to 34" tall are classified as A-division or "under" horses, whereas horses between 34" and 38" tall are classified as B-division or "over" horses.
AMHR still allows the hardshipping of AMHA-registered miniature horses into their A-division books. This means that many sub-34" miniature horses are double registered with AMHA and AMHR. The AMHR organizes the yearly AMHR National Show, the largest and most elaborate miniature horse show in the world. In recent years, many of the horses winning at the AMHR National Show are double (AMHR/ASPC) or triple registered (ASPC/AMHR/AMHA) American Shetland Ponies.
More information on AMHR can be found on the American Miniature Horse Registry website.