I've noticed that the crank rings on my Shimano Golden Arrow crank appear to be a bit loose. I got them as tight as I could when I assembled the crank originally, but I don't have a screw driver with a flat head wide enough to span both sides of the notches for the back-side nut. Thus it was very difficult to get a lot of torque on the bolt to cinch it down tight. Any handy ideas? I've thought about putting a butter knife blade in a vice and put the backside bolt on that and see if that works - but not sure how well that will go over.