The basic screw heads, minus the D-ring, are classified as a "cheese" headed. An archaic reference to a wheel of cheese as I understand it.

IMO the best bet is to contact the company and find out what they are called and where they get them. You may have to sweet talk them a bit because they are going to want to sell you the screws as replacement parts at five or ten times the cost. sure thing that SPOT does not manufacture their own screws. So there is a company out there making and selling them.