Great DIY project over at Blue Collar Mountain Biking for making a bottle opener from a cog and a bit of chain. Just gotta get an old cog and cut it up. Full directions on the site, with pics, when you follow the link.
Alternatively, if you're not a handy-person, you can just buy one in a pretty color.

I did this a couple years ago, made 6 from one cog and a chain, gave them to my riding buddies.... Very cool.
Posted by: Arron | 05/18/2012 at 11:10 AM
Awesome, but at the same time kinda scary looking. =)
Posted by: John h | 05/20/2012 at 08:18 AM