PM ONYX Steel Mainspring #55 for Benrus caliber S

PM Mainspring No. 55 for Benrus caliber S movements plus perhaps others as well, ONYX steel, new in envelope. See images for further data and precise mainspring specifications. I specialize in hard to find watch parts so I usually have whatever you might need and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.