The most popular collar buckle called as double bar buckle, you needn´t to use extra strap holder. Edges are nice finished. Use stainless steel D-ring
Stainless Steel Roller Buckle 1.5 inch By Nickel Smart® - Heavy Duty
Double Bar Buckle
Double Bar Collar Buckle 10 - 40 mm, Rose Gold
Double-Sided Stainless Steel Buckle with Keeper
Double Bar Collar Buckle 13 - 38 mm, Stainless Steel
3/4 Strap Buckles
K9Z Double Bar Buckle for collars
Specifications * Strap Size: 0.63 in. (15.88 mm) * Strap Size: 1 in. (25.4 mm)
Double Bar Buckle
22mm Decoration Hardware Metal Pin Buckle/Belt Buckle