This tool can be used to loosen that Torx-like cap, which is holding the left crankarm on the bottom bracket spindle (see picture).This is needed to swap/clean your crankset or replace the chainrings. The video here explains how to remove your crankset http://www.youtube.com/watch?v=hs_ywOIYzdY There are plenty of instructions about this procedure online.Don't be worried about this tool being made out of plastic - the original is as well.1) Print the part.2) While it is printing you can already loosen the hex nuts of the crankarm.3) Use the tool to unscrew the cap.4) You can now remove and clean/swap the crankarms.Beware that the hex nuts should be fastened with a torque wrench, so (depending on how seriously you take that advice) you're going to need one in order to get everything back together.