What useful things have you printed on a 3D printer?

[oliof]

repair / reinforcement brackets, wall holders to turn rods into hangers, all kinds of connectors; emergency replacement wheels for 1:32 slot cars, self watering plant pots, shims, spacers, wedges, skadis holders of all kinds for a sewing station, ....and some more I forgot about

[dwuk]

The most useful print I've ever done is a shoe horn -
A quick print using PLA on BambuLab printer.

Use mine once or twice every day.

https://makerworld.com/en/models/122098?from=search#profileId-131553

[bug2k22]

Many things, upgrade parts and mounts for bikes, timetrial starting clock, pool shot timer, electronic telescope focuser conversion, workshop storage bins/trays/holders, battery adapters, camera flash reflectors, speaker mounts and things I've long since forgotten about.

[DaveA]

@dc42

A set of adapters to mount deck railing lights on new deck.
Prototype plastic brackets to mock up an air conditioner compressor on a 1967 MGB. After several iterations the plastic was used as a template to cut brackets in aluminum.
Oil catch can mount for a1946 MG-TC
Several fabric holders for wife's sewing machine.
Timing gauge for wife's long arm quilting machine
Jewelry display mounts
Housing for an O2 sensor display.
And, of course, parts to update my other printer

[mrehorstdmd]

Several lamps, a bread box, bicycle disc brake sanding tool, bicycle fender mount, Nespresso capsule dispenser, Pax Plus vaporizer handle, Ikea Frakta bag handles, physical therapy rubber band handles, incandescent lamp replacement for microscope illuminator, camera and cell phone mounts for telescopes, microscopes, and 3D printer, in-drawer knife block, wire twister tool, Wago lever nut mounts, several furniture feet, a Van de Graaff generator, 3D printer spool holders, coin and wallet holder for Prius console, replacement for failed Prius trunk release cover, stand for S&B Mighty vaporizer, bottle cover for Uberlube, parts for my sand table and 3D printer, parts of a 20 liter soda syrup tank agitator, replacement pushbutton caps for an old preamp, brackets for a "cat ladder", cat puzzle toy, aperiodic tile array pieces and storage box, cutting board drying rack, dental x-ray sensor wall mount, brackets for mounting curtain rods,
racks for torx and hex screwdrivers, bicycle air horn bracket, coasters, cable hold-downs, bicycle chain guard, One Wheel electric skateboard car stand, ear-savers and bias tape making tools for COVID masks, compartmentalized refrigerator storage box, binaural mic earpieces, manual coffee grinder electric drill adapter, antique radio dial belt, Audi and BMW jack pads, white board marker and eraser holder, and many more.

Bread box and cover:

Disc brake sanding tool:

Bicycle fender mount:

Button caps for old preamp:

Lamps:

Another lamp:

Coin and wallet holder for Prius console:

[stuartofmt]

Likely the most useful was a bear spray, quick release (important!) holder. I used to mountain bike in Montana
https://www.printables.com/model/137420-bear-spray-holder

The best cost-saving was a dash component for an older Range Rover. You can imagine what the stealership would have charged!

The simplest (but nonetheless useful) was new, square, washers for a toilet seat mount .

[mikeabuilder]

My 3D prints are paired 99% of the time with a custom 3D design in Autodesk Fusion. I almost never download a model to print.

My parts:
Loads of utilitarian things for around the house - custom hangers for tools in the garage and shower cleaning supplies. A made to fit basket for the kitchen sink to hold and drain a sponge. Stands for art pieces. Cleats to wrap the pull-cords on window shades. Custom corner fittings for electrical conduit, The housing for a heater to keep the hummingbird feeder from freezing in winter. Handles for hex wrenches.

Many repair parts to extend the life of something - replacement foot straps for a stationary bike (TPU), replacement sprinkling spout for a watering can, replacement hinges (PETG) and latch (TPU) for a picnic cooler, bracket for a replacement switch.

Proof-prints for personal engineering challenges (can I design X in Fusion?) - I think these technically fall into the "artistic/ornament" category. Gear trains for a Copernican orrery, a 1ft diameter spherical shell 6mm thick (smooth on the inside and outside), various print in place sliders and hinges.

And of course, parts and accessories for a 3D printer.

[OwenD]

Apart from sundry brackets, housings etc around the house, most of my efforts are devoted to custome skirted lure designs for marlin fishing.
"Traditional" lures have a head cast from resin. Shaping the face creates a swimming action and having holes through it helps create a bubble trail to help attract the fish.
It's a big ocean out there, so anything out of the ordinary for a predator gets attention and hopefully an "I wonder if I can eat that" moment.

I don't try to replicate traditional lures. We all know they work and resin being heavier has different properties.
I try to design things that have never been tried before.
Flexibility of design and fast prototyping allow me to create weird shapes to see what they do to the action as different areas grab the water.
Easy creation of complex air pathways allow differing bubble trails.
I can combine tings like bibs (normally only used on non game fishing lures) and add pivoting sections.

Some designs work, others are abject failures , but it's all fun.
Unfortunately I don't own a game boat, so usually only do one trip a year chasing marlin.

A few designs

Checking out theaction and bubble trail

A marlin checking out the spread.
Underwater camera towed in the lure spread shows fish come for a look but often don't strike.

[zuoyan]

I printed wire spools.

Something not useful, but fun, I printed some wind turbines -- for me, this is the driven reason to buy a 3d printer.

I plan to print some stacking boxes to use corner spaces around furniture, but have not started yet.

[Superbrain8]

on my workplace i use FDM Printed parts quite frequently for Workholding Jigs.
either on a CMM or on a Mill to get oddly shaped SLM Printed parts to behave.

Printed stuff like a Door Dampener out of 60A TPU to prevent a door to slam shut during the summer months when i have a window open
also for a family member a guideblock for a Circular saw because of poor Manufacturing tolerances the included one had way to much play