These cup depth extenders are the thin, flexible Delrin spacer rings you may have read about on Tubenet. To assemble, remove the screw rim from your mouthpiece and slide the extender into the rim’s thread pocket. When you reattach the rim, you will have a deeper cup to experiment with. The effect will be more prominent on shallower cups and less so on deeper cups. These extenders offer just enough depth to tweak your sound to be just a bit darker.
They are machined from Delrin tubing and will add .160 inches or about 4mm to the overall cup depth.
This extender fits the Sellmansberger and Parker models. It will also fit the old LOUD LM10 reasonably well.