I have a Bass that I can't get the action nearly low enough and I can't adjust a truss rod anymore or I'll end up breaking it, and I've lowered the bridge as low as it can go. I've heard about people using shims in the neck pocket, but I don't know what to use for a shim to put in the neck pocket. What do people use to do this? They're obviously put their to tilt the neck backwards in order to get the action lower, but I need some help/ guidance on what type of material(s) I should use as a shim. Thanks.