The 51 is a standard unlined 1.75 inch SAFARI-LAMINATE garrison belt. It has a removable square brass or crome plated single-tongued buckle.
Sizing
Extra Small - 24-26 inch Waist
Small - 28-32 inch Waist
Medium - 34-36 inch Waist
Large - 38-42 inch Waist
X-Large - 44-46 inch Waist