5/16" nut knob, 1" outer diameter. Compatible with a 22mm or adjustable wrench.

The Kohler GP51487 tank gasket kit comes with bare nuts that retain the tank to the toilet base. Previously, my toilet had plastic nuts that were 1" in diameter. This makes tightening the screws much easier, retains the original outer diameter and keeps the ability to use a wrench if necessary.

This goes on like a washer, then start screwing the nut, then let the knob cover the nut and use it to turn.

You can also use a 22mm or adjustable wrench to turn the knob - I've retained flat sections just under 22mm apart in case the nut is stuck for any reason.

I printed in PETG, fat layers and many perimeters to create a solid object. May as well crank up the filament temp to 250-255 to increase layer adhesion; there are no overhangs to worry about.

I imagine ABS, ASA or TPU would also work well.