The Thingiverse

An alternative to making your own 3D file using CAD is to download a ready made version from an online repository

3D files come in many forms but one of the most common the .stl file.

STL stand for Standard Tessellation Language

Here are some good online resources (not all models are free):

Thingiverse - Digital Designs for Physical Objectsthingiverse

Cults・Download free 3D printer models・STL, OBJ, 3MF, CADCults 3D

YouMagine – YouMagine - Where makers collaborate on 3D designs 🚀YouMagine

Probably the most similar to Thingiverse

Discover STL files for 3D printing ideas and high-quality 3D printer models. | MyMiniFactory

Free 3D Printable Files and Designs | Pinshape

GrabCAD Making Additive Manufacturing at Scale Possible

Aimed more at professional engineers

You have to pay for the ones in CGTrader

CGTrader - 3D Model StoreCGTrader