1 point
Kinda looks like something to adjust pressure but I’m not sure.
12 points
The indentions on the side are for a spanner wrench to tighten this nut onto a threaded rod. The top is a decorative cover.
2 points
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The hole looks like it’s for a set screw to me, but I agree the cap is just a decorative cover. Not sure what this would be used for though as I don’t understand what function a collar and cap like this would do mechanically.
Edit: I see OP mentioned the holes don’t go through so you’re right they’d be for some special tool.
2 points
A couple of more pics.
4 points
i saw something like this once where it connects a tank of carbon dioxide to a sodastream type of drink bubbler.
3 points
Looks like a spanner nut and the cap appears to be a jam screw to lock it in place.
