Regular buckles that fit 38 mm leather straps. Some are 40mm buckles but they still fit a 38mm strap OK.
A 40mm buckle size typically refers to the width of the buckle frame or the opening of the buckle where the belt is inserted. This measurement is also sometimes referred to as the “buckle tongue width.” A 40mm buckle size is equivalent to 1.57 inches, or just over an inch and a half.
A 40mm buckle size is a common size for belts worn with jeans, casual pants, and some dress pants. It is also a popular size for men’s and women’s fashion belts. When selecting a belt with a 40mm buckle, it is important to ensure that the belt width matches the buckle size for a proper fit. Additionally, some belts with a 40mm buckle may have a wider strap to accommodate the larger buckle size.