Many of us have had to deal with plastic electrical boxes with stripped or broken device mounting holes. Sometimes people use a drywall screw, which works if the hole is just stripped, but may crack the mount. (and it seems like a hack)
I found these clips which are a quick and elegant solution:
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I've ordered some; will see how well they work, but I'll bet they do the job.No relation to the co., just passing along a potentially useful link...
Paul F.