Like other have said, they are mostly held in by friction. I had to Dremel the gauge openings larger, and I just went really slow, and test fitted the gauges often. That way I could get them to fit really snug. I'm also going to use the retainers that came with the gauges. For the small gauges I can use them as is. For the 5" gauges I shortened the retainer, and notched the top of the plastic panel. That way I can get the retainer to sit flush on the plastic.
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