Those mystery rubber nuts are called well nuts.  We use them installing thigh braces in roto molded plastic kayaks and they also attach the drain plugs to the deck.  I've never seen one bigger than 3/16", but they may exist.

Dimwitted Moose and Flying Squirrel    90 GL  Millennium Falcon III   132k
    -----Original Message-----
    From: Fitz-Randolph, Douglas <dfrandolph@TALKAM.NET>
    To: vanagon@GERRY.VANAGON.COM <vanagon@GERRY.VANAGON.COM>
    Date: Friday, May 14, 1999 12:32 PM
    Subject: Mystery Metal fastener...
    
    
    For the life of me I can't remember what they're called, but they've got them in the "Fasteners" section at my local HQ (Home Quarters - big store like Home Depot, only green instead of orange)...

    They're like short rubber tubes with a flange at one end and a nut embedded at the other. The dia. of the tube should be the same size as the hole in the metal. Push the little gadget into the hole - the flange keeps it from going all the way through. Insert an appropriately-sized bolt and tighten - as the tube compresses, it gets wider and eventually makes a tight seal in the hole and flares out behind it. Mind you, I haven't seen these things in very large sizes and I'd say they aren't made for high weight or stress applications, and you can't tighten them *too*  much - but if it's just a piece of plastic trim you are fastening, it might do the trick.

    I first encountered them on my motorcycle where they're used to attach the windshield to the fairing (all plastic), and I'm currently planning to use them in place of those nasty plastic trim clips that hold the interior panels to the body of my van during it's upcoming renovations

    Doug Fitz-Randolph 
    Yarmouth, ME 
    dfrandolph@talkam.net 
    '90 Syncro 

    [sorry about the HTML...] 

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