This special star-shaped nut is commonly used for gripping weight wheels to dumbbell rods.

RepRap

Graber i3

No

No

0.2mm

30%

RECOMMENDED SETTINGS: print with no support, 0.2mm. Use a medium to large wall thickness and infill for improved resistance, specially if printing with ABS. I recommend at least 5 walls (top/bottom also) and 30% infill. If you print in polycarbonate you can use a little less.

I strongly recommend you use a hard filament to print this design. ABS will do fine, but polycarbonate is even better. If you print in PLA it will probably be too brittle, don't hold me responsible if it breaks.

I have a couple of dumbbells at my home gym and the star nuts holding the weights were getting loose. I tried to find the exact measurements of these nuts on the net so that I could model or buy some extra parts, but I couldn't find it anywhere. So I grabbed a caliper and just measured the thing, then gone through several iterations (8) until I got a part that fitted exactly on my dumbbell rods.

Although I could not get the measurements online, from pictures it seems that most if not all dumbbells use the same screw sizes - even the pitch and the spiral direction seems to match. So I think it's highly likely that this design will fit on other dumbbell brands.

I have used the public domain library polyscrewthread, which I include here. Just put it in the same directory and it should work.

I have made two versions. The first one is the final design which I printed and fitted perfectly on my dumbbell. However, I have a FDM printer which "overextrudes" about 0.2mm outward in the horizontal plane due to the 0.4mm nozzle. So, if you use a non-FDM printer which does not everextrudes, or you use XY compensation in your slicer, or you somehow manage to get exact measures with what you print, I also made an "-exact" version which has "exact" measurements for the nut to work. So, if you print the nut and it is too loose, you might try this one which has a slightly smaller hole.

Also, if you are reading this and you know where to find the measurements information that I couldn't find, I'd gladly thank you for telling. :)