The HP N91774-001 VESA mount plate with VESA cover is a mounting part listed for the HP 524pu. It brings the plate and cover together as a part identified for this monitor model.
The plate is intended for VESA mounting, while the included cover is part of the named assembly. This item is identified specifically for the 524pu; the listing does not provide dimensions or further installation details. Its purpose is to provide the VESA mount plate and cover associated with that model.