Two knob models which go over the pots on my JR 8103 radio control transmitter. They help you know the radial location of the pot/dial on the TX while flying.The inner diameter is made exactly so you can force it down on the knob. You may need to increase the inner diameter on the bottom with a sharp knife. It needs to be built without a raft. Knob1: simple thick outer diaKnob2: has beam on top, and also flattened sides for extra 'feel' while flying, model has a top beam which sags a bit due to the air bridge.