ImplicitCAD is a free open-source 2D and 3D design tool maintained by Julia, and now it’s available as a web-based service. It’s text-based and parametric. Head on over to https://implicit.faikvm.com/ to see a demo and design your own parts and objects, then download them as STL and 3D print them. For example, this is a child-like artistic impression of a bolt that would not work very well at all (feel free to click the link and improve it though):
union() {
cylinder(r=19, h=10, $fn=6, center=true);
cylinder(r=10, h=40);
rotate_extrude(4*360, translate=[0,38])
translate ([10,0]) square([8,4], center=true);
}
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