Oh boy oh boy....I learned a lot from these guys here on this one!
If you mean on the side of the block, thats a freeze/expansion plug.
If you mean the domed looking device on the front of the block just below the water pump, thats a core plug, not a freeze plug, and its an entirely different animal than a freeze plug.
Chevs of The Forties sells the whole set for around eight bucks.
Only thing different is the core plug goes in concave facing out, and is kept in place by denting the middle with a few good whacks from a socket smacked with a hammer dead center, also use a good sealer with them.
Either core or freeze plugs are easy to change, good luck!
