you can tell for sure about the peanut plug for the machine work around the hole

peanut very little machine work. my pinky in the hole.

plane jane head has a nice flat area around the hole with clearance for the fat washer/body of the 13/16 plug. my thumb in hole.

when I swapped on my plane janes I used the peanut 5/8 plug in the the flat washer 13/16 hole for about 2 weeks till I could pop for new plugs.

they sealed and worked fine. I did not notice them leaking or anything. BUT in a pinch I did get by.

** just cause I got away with it does not mean it is right.