The idler cages are fairly thin metal. The rule of thumb for screws is that you need an engagement length as long as the diameter of the screw plus one thread. This allows you to be able to develop the full strength of the screw. However, given a fairly small screw size and thin material, it could be safer to use low torque and a threadlocker rather than higher torque alone. I would think that it would greatly reduce the chances of striping the threads.