This is a simple fire extinguisher wall mounting bracket. The downloadable STL is for an 80 mm diameter extinguisher. If you have a different size, open this in customizer and make one that works for you.
As soon as I finished the model I thought of a lot of ways I could tweak it to make it stronger and prettier. But by then I had a wall mount that worked. If you feel like modifying the design please do. I think of this as a first draft that works.