a nickel will not work. I reccommend going to your LBS and asking to buy one, or borrow one if they wont sell it to you. I borrowed one from Mesa Cycles in STL (Thanks Mesa.. you guys are awesome) a while back. The peice is a solid steel "tophat" looking peice.
I actually tried a 2 eurocent coin originally, but the coin bent and it honestly caused me to almost hae to drill it out. Get the tool...dont break your cranks trying some other wackjob method.
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2008 Cannondale System Six
2016 Pivot Mach 5.5