If you don't want to create your own 3D design, there are online databases of 3D models that other users have created and submitted for public use. Sometimes the part you may need for your project has already been designed and is available for free from one of these databases.
- The most popular place to find 3D models. The models here are designed to be 3D printed, but are user-created, so their quality can vary. All models on Thingiverse are free!
Still can't find what you're looking for? All3DP has compiled a list of the best places to find 3D files. They're even ranked by file quality and other criteria.