https://www.adafruit.com/products/775 for $17.50Shouldn't be to hard to mount a plate to it, There are larger ones as well.Hope it helps you!
this seems to b 1 method to do it:http://en.wikipedia.org/wiki/Slip_ringthey claim to b better:http://www.mercotac.com/html/faqs.html#q1 (but they r not RoHS compliant because they use mercury... )
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