Does anyone know what diameter the Columbia Side Mirror supports are? Are they .5 or .75 inch by chance? I have a portable XM Radio but my antenna is broken and I'm looking at buying a truck mirror mount bracket so that I can place my new magnetic base antenna on it as I slipseat every day. Also does anyone know if they make a spring clamp type mounting bracket. Any help would be appreciated. I found the truck mirror bracket on Radioshacks website, it is made by Terk.