The trouser leg function is performed by the "Kool-Stop Chain Disc". They come in a couple of sizes depending on the tooth count of your chainring and they mount with a center screw which goes into the crank arm hole so that they are agnostic of the chainring bolt pattern. I Have two and spent a few minutes with WD-40 and my fingernail taking off the dorky logos but they work fine and don't make noise. I had to open up the clearance slot a little for one crank but that was just a few minutes work with my Dremel.