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goggo said..Went out yesterday on old 7m, fell off hooked in, snap.
(I'll explain in rather basic terms since this is not a 3D printing forum.)
It looks like your print is almost entirely hollow. 3D printing has a bit of a problem in that the models are typically distributed as STL or 3MF files, which describe the geometry. If the designer wants to leave something hollow, that's possible. However, if the designer puts a huge solid chunk somewhere (to make the part strong), the person doing the printing is still going to run that geometry through the slicing software that converts the shape into a series of instructions for the printer. It's done this way, because the instructions are always specific to the printer and filament used.
Most slicer defaults however are not made to produce particularly strong parts. They aim to produce prints that look like the model that was sliced, print reasonably fast and not cost too much in terms of material. This means solid areas inside the print usually end up almost entirely hollow (maybe 10% density).
I haven't made a harness hook model, but on Sunday, I released some new models that have very high durability requirements (at least for plastic 3D prints), so I made sure I gave some guidance on how to set up the slicer to produce a strong print and I'm giving a weight estimate on how much the produced part should weigh. That way if you're printing my design and the weight is only half of the ones I'm printing, you'll know something is probably a bit off.
Check out the "printing details" section to see what I mean (this is a screwdriver handle that I designed for assembling hydrofoils):
www.myminifactory.com/object/3d-print-gyrokey-classic-revolutionary-screwdriver-241639The shell thickness is generally more important than the infill density. If I want something printed fast and durability doesn't matter, I just print with two outlines and 3-4 top and bottom layers. That means the side walls are 0.8mm thick and the top and bottom are about 0.6 - 0.8 mm thick. Once you go up to 5 outlines or more and 10 top & bottom layers, you're entering the "oh, this actually feels pretty sturdy" territory. For the Gyrokey screwdrivers, I'm doing 10 outlines and 10 top and bottom layers and 40% infill. The surface quality actually takes a bit of a hit because the print is so close to solid, but the print time is still pretty reasonable and the extra durability doesn't add much more than 20-30 cents to the material costs, so it's well worth it.
When I designed the Duotone-compatible boom heads, I made the parts hollow on purpose. My first prototype was solid, so the durability was entirely up to the slicer settings and I actually went a bit overboard and ended up with a rather heavy front piece. Making the model hollow by design means you can crank up the slicer settings pretty much as much as you like and it's still going to print with about the same amount of material as the ones I have been using here all year.
If I slice the harness hook from Thingiverse using the same settings I use for the Gyrokey, I get a weight of 59 grams.
BTW, using TPU (like the author suggests) is not a bad idea, but it's then really important to print the part almost entirely solid or it will be too floppy to actually work as a harness hook. TPU (thermoplastic urethane) and TPE (thermoplastic elastomer) are flexible filaments. They bend really easily and potentially stretch a bit, but they don't crack like PLA (PLA is really rigid and can be a bit brittle). If you print a moderate to low flex filament thick enough, it will be pretty solid and I could see how it would potentially work quite well as a harness hook. With default slicer settings though, you're likely to end up with a wet noodle for a harness hook if you use TPU/TPE and a fragile hook that can not take the stress if you use PLA.
The beauty of 3D printing is that if you find that something you made isn't strong enough, you can potentially change the way it's printed or use a stronger material.
I hope this helps.