PURPOSE: To perform the positional adjustment of a mark correctly and easily, by providing a serration part and a mark consisting of a graduation and datum line on a base and end part block.

CONSTITUTION: A serration part 50 where a lot of teeth are arranged in the longitudinal direction is provided on a support face (base) 1 and teeth 51 meshed with the serration part 50 are provided on the end block 4 for performing the positional adjustment in the longitudinal direction, of end blocks 3, 4. Marks 52, 53 for showing the relative longitudinal position of both are provided on the end blocks 4 provided with the teeth 51 and the base 1.