This is a replacement knob for the Akai Force's main encoder (data dial). Mainly I hate how the encoder is very slow (few clicks per revolution) so you have to turn it several revolutions to edit a parameter, but the stock knob is too small to spin, so you can't turn it a whole revolution in one movement. I've made this knob more like a jog wheel: with your finger in the little depression, you can spin it freely.
It's the usual 6mm D-type shaft so the knob would fit other instruments too, but I sized the base to fit in the "bed" that the Force has around this encoder. (That is, the base is the same diameter as the base of the stock knob.) There's no need to have this shape on another instrument.
The picture with one dimple is the original design. It's a bit too wide so if you push down on the edge of it, it doesn't click the encoder properly, it just bends. It also doesn't fit under the Decksaver for the Force. For those reasons I made a Mk2. The three dimples make it easier to spin around, and it's slightly smaller in both dimensions. You can use it with the Decksaver and it clicks the encoder a lot more smoothly.