The caster block is the C-shaped part. They have a number and letter on the inside edge (eg R6), which indicates the side and caster angle of the block.
The hinge pin blocks are the parts that the suspension arm mounts in on the chassis. The standard setting is 2deg, but if you turn the front block upside down, you get 0deg.
The total caster angle is the sum of the hinge-pin setting and caster block.