The bathroom faucet started moving loosely. Found that both locknuts had broken off. Instead of spending 1-2 dollars for a new locknuts, I designed and 3D printed new ones because my printer is a proverbial hammer looking for nails. I also had issues disconnecting the hoses because I didn't have good tools to deal with the tight space in the cabinet. I thought it would be easier if they were wing nuts, so I made attachments to make them easier to retighten (and untighten later).

Demo at https://youtu.be/Yg4gn-w42bg

Printing

Recommend printing with PETG. PLA IS HIGHLY DISCOURAGED. When hot water is flowing through pipes, PETG should be outside the limits of deforming from heat from long-term use - at least in theory, assuming the water isn't hotter than scalding. PLA is closer to that temperature.
(Deforming/distortion temperature shouldn't be confused with glass transition or melting temperature)

No supports are needed. Models should already be oriented so that the correct side is lying on the bed.

No special printing instructions. I printed at my slicer's default 15% infill. Although the original locknut is injection molded (which means it has 100% infill), 15% felt fine: rigid enough and I figured some flexible give wouldn't be bad for a locknut tightly pressing against porcelain.

Locknut

Two versions are included; the Loose version has slightly more thread tolerance.

The locknut has bigger dimensions than the original one I'm replacing: larger radius, taller, wider ears. This makes the body "unstandard" and may not fit in some places or work with some tools (like engaging with locknut wrenches).

Wingnut

Two versions are included; the Loose version has a slightly larger socket radius.

Fits a 7/8" wrench sized nut.

The wingnut cannot be removed from the hose unless the hose is detached. But it can be slid off the nut so that it doesn't make direct contact with the nut (and absorb that extra heat from hot water) after it's used. When removing the hose later, it can be slid back on.

Source

Blender source included.

The Blender source comes with an embedded text document with a few notes. Requires the Precision Bolts plugin with a Blender version compatible with it (in this case, Blender 4.0) . If you don't have the plugin, you'll still have the geometry, but won't have the ability to edit the threads parametrically.

Warnings

Not a plumber or material scientist, so providing these designs and the write-up is not plumbing advice.
Make sure threads are not too loose or overtightened.