The M. Toulouse Tom Thumb 1/2-inch Neck Spur measures 1/2-inch from boot to tip. USEF rules state to measure the spur from the base of the spur to the end of the tip.
Maximum spur length is 2-inch or 5.08 CM. FEI rules state that the spur can not be longer than 4 CM from boot to end of spur, except for FEI Pony Riders and Children are limited to 3.5 CM with no rowels.