Tooth Changing Gears

[MrForbes]

Yes you could use a key, or you could use gears with a hex hole, and a hex shaft to connect them.

Some of these gears have hex broached holes in them

http://www.andymark.com/SS-Gears-s/209.htm

Look around on the AndyMark web site, there is a lot of useful stuff there!

[PAR_WIG1350]

I recommend the AndyMark cluster gears and cluster shafts which are specifically designed to be used to put two gears on one shaft without spacers (be careful, if the parts don't come from the same transmission family, spacers or machining might be necessary to get them to fit on the cluster shaft).
http://www.andymark.com/Hex-Shaft-Gears-s/237.htm
http://www.andymark.com/Shafts-s/266.htm
the super shifter cluster shaft is named as such, but the tough box cluster shaft is simply called the Toughbox Small Hex Shaft.

[Nick LaPosta]

Cool thanks. I have been struggling with the idea for a few days and never thought of this