Measure the frost plug opening with a caliper and compare the outside diameter
of a new frost plug.
Want to make sure the frost plug opening has not been opened up where someone was trying to remove surface rust and pits.
If there are steel frost plugs in it, I would knock them out and put in a set of brass ones as they are a little softer and will grab better.
Want to make sure they fit snug when tapping them in with a socket that just fits inside them.
Brush on a coat of High Tack Sealer on the new frost plug and the block opening before tapping them in.
