On Sun, 24 Jan 2010 13:36:42 -0800 (PST), mac
wrote:

My Garmin NUVI 500 for my bicycle uses a ball mount. The one that I
purchase from a third party is hollowed plastic and broke from
vibration. I adapted the broken piece to my light bar and it broke
again at the ball.
I toyed with several methods. One buy a ball turning tool, two find a
ball and mount it to a post. The ball was .670 inches and I didn't
find any one that size.


It would have been 17mm


Mark Rand
RTFM