It's probably a 1 1/8" flat freeze plug. (1.125") If one of them is a little too big, just grind or file the outer edge until it's a close slip fit into the counterbore, then a firm tap with a hammer will lock it into place.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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