These keycaps were officially made by Cherry and were intended to be used with their old G80-04xx series of keyboards or home-made keyboard projects. The set only features the entire number block, as well as some other math related symbols. I found these NOS still for sale at one German electronic parts distributor. They are most likely intended to be used with the much older, open variant of the Cherry MX switch, but they still fit the modern ones just fine.
