This is pressure fit to your bl-touch to keep the probe pin clean and to keep strings and webbing from getting into the path way the probe pin moves in
Alot of people start to have issues with their probe sticking, not deploying and just becoming unreliable
Every one of these i've seen was because the probe pin or the path way of the probe pin had stringing/webing in it. Alot of times you can just barely see it at all.
This should keep that from happening as well as possible protect the probe pin itself
Just align the pin with the hole and press on
tolerances are tight so if your printer is not well calibrated you may need to open the hole a little I only gave 1.5mm of room for the pin to help keep anything out
As always I accept tips