I am so glad to perfect a vintage collar necklace by replacing the clasp by a belt buckle I have for more than 10 years. 
The buckle itself is an art deco piece with rhinestones in round and table cut. Collar necklace with 5 strands of metal chain and huge synthetic pearls in substantial weight. 
Shortest 43.5cm / 17'
Longest 59cm / 23'