Anyone ever seen a fastener like this? More importantly what type of tool installs/removes this? I have a store nearby that sells surplus aircraft industry stuff, and fasteners are by the pound. Wasn't paying attention, and thought it was a dirty phillips head, so I bought a few pounds worth. Useless unless I can figure out how to drive them. Obviously something to do with the underside of the head, but I'm lost from there.
Markings on the head appear to be "SPS" over an "s". Or maybe "SFS" over an "S". Nothing else I can find in the way of markings.
Anyone?



Markings on the head appear to be "SPS" over an "s". Or maybe "SFS" over an "S". Nothing else I can find in the way of markings.
Anyone?
