Pacific Pearls in Japan used silver clasps for over 99% of finished necklaces, including high end. In the 1960's and early 1970's, this was inevitable because a luxury tax (50%) was levied on gold items in Japan... it could be refunded with evidence of export, but that was cumbersome at the time and required pasting a form into the customer's passport. The selection was also quite limited. The Japan origin silver (manufacturing has since been driven out to Southeast Asia by costs in Japan) was 925/ooo and the plating lasted years with gold (ie vermeil) and decades with rhodium. The requirement that the snapper be of the same alloy as the box of the clasp was a problem because silver snappers tended to lose their springiness and require re-tensioning with pliers. After it became legal to sell silver clasps with steel bladed snappers, the rhodium plated silver clasps for the Japan market became the most durable and trouble-free option, the best value for money in our opinion. Many seem unchanged after years of use. Given the recent gold price, the need for clasps that are substantial enough to function well at a silver price is undiminished.
We use silver rhodium plated clasps from a Japanese company manufacturing in Thailand. Gold plated silver (ie vermeil) clasps we source in Japan, and India style hooks in US. The former probably are 85 or 90% silver, the latter at least 70%.
We believe it is more important that we have been able to weed out a lot of lemons, insist on soldered jump rings for durability, and upon a mechanism that works without looking.