As I recall, there are small clips that hold the vent (funnel shaped piece that connects to the vent duct) up against the vent opening in the dash. Perhaps that is what you are referring to. There are two on each side.
Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix