To assemble the window regulator motor to the window regulator, I decided to use 1/4" mate rivets. I could not find a retailer that had the Avdel mate rivets in stock, so I went with Hanson CM-ASA814 1/4" diameter, .750-.875 grip, mate rivets with steel mandrels/aluminum bodies. (Edit: On second thought, these may actually be the Avdel rivets.)
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Assuming I measured the thickness of the window motor and regulator mounting locations (3 total) correctly, that should be the correct grip to secure the two together. Again, don't want to use nuts and bolts. The mate rivets won't be here til next week though.
These are two of the three spots for the mate rivets.
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I don't know that those are mate rivets, but that's the closest thing I could find.