This is a disassembled Compression valve. Starting from the top:
Nut to hold everything together.
Hard to see spring and cupped spring holder, this is the top of the one way valve, flip over to install.
Spacer.
One way valve washer, moves up and down on the spacer and is held closed by the spring.
Piston, oil flows through this.
4 thin washers that make up this stock “stack,” they bend to control the flow of oil through the piston.
Spacer.
Comp valve holder, slow speed oil flows through the hole in the center.
The rebound assembly looks almost the same.
The part that does the work is the washer stack. Back in the day, pistons restricted oil flow and had to be replaced but now days the pistons flow more oil than is being displaced so it’s all about the stack.
We change the stack to get the damping curve we want.