Magnetic Drain Plug - Will This Fit?= YES it will.
 

OK guy's,gal's and others,
The answer is 'yes it will fit'.

http://i1023.photobucket.com/albums/...ps1d86b38b.jpg
17mm socket with the magnetic oil plug (Left side drain plug on a 50cc 139QMB)

http://i1023.photobucket.com/albums/...ps3d0458c6.jpg

Installed after test drive, look's good and no leakage.
Old drain plug and Dipstick shown above, at no cost to you. ;)
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I did however need to "work this drain plug into place a bit, but not so much as to "chase the threads".
The Magnet is quite strong i picked up a 3 pound hammer with it just as a test.
The link to the Ebay seller shipped in a timely fashion.
I payed $18.99/free shipping, but i see the price went up a buck. humm..

http://www.ebay.com/itm/RARE-EARTH-M...999423?vxp=mtr
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Matt.. PFS.. you need to look into stocking this or one real close to it.