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Yes, they're 1"...
https://www.ebay.com/itm/Melling-MPC-16B-Brass-1-Deep-Cup-Expansion-Freeze-Out-Block-Plugs/202806239986?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
IIRC, you should be able to smack those on an inside edge with a punch and get them to pivot in place, like a...