Mechanical interface of motors

I think the "flat" you refer to is the groove-like surface they put onto some motor shafts to give a grubscrew in a gear bush mounted on that shaft something to lock against - if you try to use grubscrews on smooth nshafts for heavy duty work, they tend to slip round the shaft, making a right mess of it. Generally speaking, flattened sides on output spindles are used for slow speed, high torque motors, and smooth spindles for high speed motors(probably so that, if the machinery jams or seizes suddenly, the slipping of the gears on the spindle will absorb some of the angular impulse and lessen the damage to the machinery), but they are sometimes used in these too.

Tom

OK, I understand. Now how am I supposed to mount this to anything? I don't see such screwable parts anywhere. The only solution I can imagine is to glue piece of lego to end of shaft and continue mechanism from there. But I would like to have some cheaper part that could be reversibly mounted to motor and glued to lego.

Hi Robert, Although this web site doesn't match your particular problem, it might give you a few ideas on how to solve the problem you are facing. "A procedure to attach a baby stroller wheel to an automobile window motor."