These are captive quarter-turn Dzus assemblies, The flat-head 5/16" diameter stud is permanently assembled to a compact mounting plate. The stud is spring-loaded. This self-ejecting prevents losing body panels. It also make it easier to install big body panels.
The plated stud assembly is designed to be riveted to a panel using two 1/8" diameter rivets . the rated strength is 85 lb. in tension and 200 lb. in shear. Overall stud length: .42 inch. (working) length: .30 inch. Head diameter 5/8". spring receptacles are sold separately.