Sacrificial plates to protect the bed of a mill when machining through small, flat workpieces. A lip along one edge allows the plate to be aligned with the edge of the bed, and the work to be aligned with the plate. This makes it much easier to square up the work than if just using scraps of wood to protect the bed.
The design is intended for the "P1" size 6.4mm Natural MDF. There are several plates of different sizes on the sheet. They are sized to cover the bed of a Sherline 5400 mill but would suit any similar machine.