As others have said: It's a 2-piece design made by Record who called it "Stay Set" (and put "SS" on their lever caps on planes that have that design of cap-iron). Record produced the Stay Set from 1931 to 1964. Clico re-introduced the 2-piece when they began producing Clifton bench planes about 2001. Clico sold their plane making division to Thomas Flinn in 2014 (shortly before going under). Flinn dropped the 2-piece cap-iron shortly thereafter - so it is no longer being manufactured.
When I wanted a No.8 sized 2-piece cap-iron several years ago (Clico stopped making the No.8 size about 2008) I had to get one from Germany, as UK sellers tend to get their supplies direct, while foreign retailers would have their own stock. So if you want to buy more you may need to import them.
I think they're a great design - other opinions may differ :wink:
Cheers, Vann.