I wanted a 3D printable O-Ring that could be parametric so I could easily change the size of it to fit different breeches or applications. 

I printed these In a soft TPU with enough perimeters to fill the entire thing. this made these SUPER stiff and hard to install on the breech. Possibly fewer perimiters and 0% infill would do the trick.

Included is the STL file for an O-Ring I designed to be compatible with the SPAMF, Nexus Pro, Aeon Pro, and other such blasters! As well as one for the T238 V2 Grenade!!!

How to adjust sizing:

1. First open the f36 file in Fusion 360. 
2. Click on "MODIFY" near the top and in that menu click on "Change Parameters."
3. Input the ID and OD of the desired O-Ring. (that is Inner Diameter and Outer Diameter)
4. The operations are adjusted so the computer should automatically take care of the thickness of the O-ring and adjust it from there. All of the fillets are mathematically generated too so the only thing the user needs to change is the ID and OD.
5. Viewed from the front, the O-Rings have two variants. The one on the left has had the bottom edge flattened to make it easier to print while the other one is a true O-Ring.

Enjoy your new O-Rings!!! Happy Printing!