those are sheet metal flange nuts, should be able to find some at NAPA or other FLAPS, probably on the 'Help' rack

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics