A pair of the spring clips for holding the glass in place. These clips can be used on all 4 corners of the bed, or on the back two corners as preferred.
These are official Ultimaker spare parts, compatible with the following printers:
Official Ultimaker Spare Parts for the Ultimaker Original and Original+. Complete set of 4 long and 2 short MXL belts.
Not compatible with Ultimaker 2.