One of the coolest applications for 3D printing in my book is the ability to produce spares on-site.
This isn’t one of the most common consumables (and it’s untested at this point so who knows what will happen), but I thought it was a good example because it took all of 15 minutes to design, 20 minutes to print and saved the time, trouble and cost of having spares shipped around the world.
Replacement bolt for crossbow ( Amazon link ). Design files on Github: https://github.com/jjg/xbow_bolts
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// jjg