Hi,

You could try finding pipe threaded plugs that have a hex or Allen internal socket in the center.
Then you can use an Allen head bit made into socket wrench with a ratchet.

Most industrial hardware places have pipe plugs with square heads.
You can try McMaster Carr or the Fastenal company that cater to plant maintenance departments.

These are used in places where a flush appearance is wanted or linkages or something else has to pass in front of the plug hole.

They are usually made out of better quality steel.
They cost a few cents more but they will a be better choice than any funky plumbing parts down at Billy Bob’s hardware!
The plumbing industry goes out of its way to make things as thin as possible and out of garbage materials. They make things just a little too odd ball so nothing else fits or to be as cheap as they can be for their profit margins. The next thing their out of business or obsolete.

Yep! Square heads are from the of many years past.