First time poster and apologies if a stupid question, but am trying to fix a leak from a radiator valve on a pretty old radiator and the cap is kept on with a strange type screw with two holes at opposite sides and am hoping for some advice on how i remove this. I have done a lot of google searches but cant see any other caps held on with something similar, hence the reason for this posting. It looks like some sort of key would be required but I don't know what. Please see attached picture Any help would be appreciated