register-plate

from The Century Dictionary.

• noun In rope-making machines, a concave metallic disk having holes so arranged concentrically as to give the yarns passed through them the proper positions for entering into the general twist.
• noun A plate from which sectors have been cut out at intervals; a plate used as the valve for a register so that the sectors close openings in the plate behind the sectored one, when the latter is rotated through a small angle.
• noun A valve formed like a gridiron with essentially rectangular openings which are closed by sliding a slotted plate over a similar one behind it.