Top Eurosport racers often glue their spur gears to their axles to prevent them from coming loose during races.  Placing the gears consistently in the same location is important.  This jig allows you to place an axle on the top of the jig, then slide the gear on to the axle in the same place every time.  Each jig has spots for 2mm and 3/32 axles.

The jig also has two holes for inserting complete gear/axle sets and drilling holes to lighten the gears, using one of the various gear drilling jigs.  Putting the axles in this jig for drilling, allows you to use a drill press, table, or hold it in your hand, without risking your fingers, and helping ensure you are drilling perpendicular to the gear.