cover-platen. a plate serving as a cover; the removable plate of a lock, a cap-plate or cap.
ΚΠ
1678 J. MoxonMech. Exercises I. ii. 26 Place the Cover-plate..so as the Centre of the Cover-plate may stand directly over and against the centre of the Main-plate.
1833 J. HollandTreat. Manuf. Metal II. 194 The cover-plate..which will just cover the opening of the box.