= Good friction on levers =
For friction locks, eg, throttles try plastic "bread cutting board". They are usually made from Polyethylene, either PE-LD (Polyethylene Low Density), PE-HD (High Density), or maybe even UHMW (Ultra High Molecular Weight)
Several People have been using it, and I don't remember who first came up with it.
I think it was me, below is an example of a prototype - tightening the screw adds friction. The discs are cut from the bread cutting board by an adjustable "hole saw" attached to a power drill.. Handy and easy to do. The knob is made from PolyesterResin and it was just "cast" inside a plastic cup used for cough medicine. The throttle shaft has a bolt attached and it has a few nuts and washers that are now inside the resin - I dont think it will ever become loose 
-- Tuomas
