Birch

This block is, I guess (I am no carpenter), birch. Hard and dense. Found it in the workshop under the table.

I guess I make the "mover", wooden block from which the front and  rear boxes hang from, out of birch. It's perfect, finnish stuff, and as said, hard and dense.

The option is plywood; found also bigger plate of 40mm thick plywood (kinda thick?!) it's also very hard and feels pretty rigid. What we require from material, is that it should not be soft since it's in constant touch with the steel rails, the rails rubs it, and the block is always being tightened against the rails with bolt...

The block is made of 8 pieces but 7 could do, the small piece of plywood between two bigger blocks should be part of the lower block. So maybe I'll just gnaw 3-4mm groove, so it'll be like _|¨¨¨¨¨¨¨¨¨¨|_ ... the point is, the grooves will force the block to be in right position

Hey, it's really hard to explain things like this in English.. I am no English speaker. Many things are easy to explain, but these PRACTICAL things here are way more complicated..