You might be able to drill a hole in your frame, where you want to mount them, so that you can screw two of the pieces together in each assembly, one on each side of the hole. That way when you screw them together they should hold them selves in place. That might work, but my team has always used zip ties in the past.
Here is a picture showing the two assemblies we need to mount. I believe we have a bracket that attaches to the regulator shown on the left; it’s the PSI gauge, sensor and relief valve on the right that I’m more concerned with. Our team likes to not design using zip-ties, just a preference. The strap may work, but I would be concerned that the assembly would bang around during a match. Anyone else have any ideas to mount these rigidly? Ideally, the gauge and relief valve knob would be pointed up for easy access…
We try to minimize the number of brass parts we use as much as possible (in favor of push-to-connect fittings) to reduce weight. We usually only use a single brass tee, and use that to mount the high-pressure gauge right next to the regulated gauge. The pressure switch goes into one of the accumulator ends. Somewhere on the high pressure side we use a push to connect tee, and mount the manual vent valve right next to the main breaker.
We also mount everything with zip ties, as this photo from our unfinished 2007 robot shows.