That one's a straight bolt thread, not a tapered pipe thread. I believe it's a 5/8" coarse thread. I've seen people plug the hole by putting a copper penny into it and installing a shortened Allen bolt on top of it. You might have to file or grind the OD of the penny a little to make it drop into the hole.
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!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!