They are brass freeze plugs,there is a sealer around the edge of them.The machine shop installed them.

1951 3100 Chevrolet
1951 Chevrolet Suburban Carryall
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"A house is built with boards and beams. A home is built with love and dreams."
"Look deep before you leap !!!" / "Everything is Everything"
"If I say a mouse can pull a house, hitch him up"