A small design detail in a dobsonian telescope is a method to restrain the mirror box in the center of the rocker box, to keep it from sliding side-to-side in the elevation bearings.
A common solution is to use a couple carpet pads to provide a lateral support that keeps the wood from rubbing. The pads do not add any friction that would keep the scope from tracking smoothly at high power. These pads are available in most hardware stores in both sheet form as well as pre-cut circles, usually one inch in diameter.
I have had trouble with these pads in Deep Violet. They do not stay put! Sometimes when inserting the heavy mirror box into the rocker I would catch a pad and simply shear it away from the wood. I ended up using a larger pad and using small wood screws to secure it instead of the adhesive.