Modeling parts for engineering and design projects is time consuming. And it can lead to parts being machined from scratch that could easily have been sourced with some slight adjustments. But the question is where to find those parts. What sites can both provide a good 3D Model and then potentially provide the actual parts as well. Here is a list of sites that provide the best 3D models and a couple that can actually provide the manufactured part affordably for that model.
McMaster-Carr has been providing 3D models of their parts for years. Not all of their over-hundred year history but a for a good part of the time CAD has been used.
Most Parts in the Mcmaster catalog can be downloaded in a number of different formats ranging from editable STEP to Solidworks files. This makes them ideal for finding and integrating parts into CAD and engineering projects. And when you are ready you can order the parts directly from McMaster and they will arrive in 1-2 days.
Part Mason is similar to McMaster-Carr. They also provide 3D models for CAD and 3D printing and can deliver the physical parts as well.
The difference is that the hardware found on Part Mason is explicitly designed and optimized for additive manufacturing. This allows you to download the files and immediately create functional physical prototypes for your project. Then as you scale up into production Part Mason can provide the manufactured pieces as you need them. Part Mason is a digital inventory of functional plastic hardware.
GrabCad has no manufacturing or supply capability. But the site does provide many free models created by professional CAD designers and engineers. While the designs are not all entirely hardware when compared to Mcmaster of Part Mason, GrabCad is an excellent resource for more complex CAD files and potentially creating relationships with high quality engineering design talent.
GrabCad also has the advantage of designers sometimes providing raw CAD files and editable versions from most different CAD programs. So it is possible to find a design that can be directly edited rather than modified from a STEP file.
Another repository of free and paid 3D models. Cults3D is a fairly informal place to find 3d models for 3D printing. Most models are more hobby based. But there are some functional pieces that have been created that can be implemented into professional engineering projects.
Another website dedicated to 3D printable models. MyMiniFactory is one of the most professional. With free and paid models the site gives a wide selection of toy and design-based models and projects that can be created with additive manufacturing.
The advantage that MyMiniFactory has over other repositories is that their models are all guaranteed to be 3D Printable. Since the entire collection is heavily curated.