Fasteners to hold down engine compartment hatch at bottom of cockpit?

Hi All,
I'm trying to fix up a salvaged Contessa 26 from about 1976. All the fasteners used to hold down the fiberglass hatch over the engine compartment are gone. They appear to be some kind of snap fitting (possibly plastic as they may have sheared off) pushed trought 1/2"holes in hatch and deck, and likely turned to lock and to put presure on a rubber gasket around the edge of the hatch. Does anyone know what these were and where I might source them? If not do you know what they look like?
Thanks for any help