This is the standard Intel socket 478 motherboard retention bracket which is the part that holds the heatsink down. The four ears for attaching the spring clips are easy to break off the plastic ones and if you have done so this handy metal replacement part will solve your problem quickly and is unlikely to break again. The plastic version is discontinued and sold out.
Product includes top bracket, back plate, and 4 screws.
Top Bracket outer dimensions:
89.6mm (3.527in) x 78.1mm (3.072in)
Bottom plate outer dimensions:
89.2mm (3.512in) x 73.45mm (2.891in)
Master carton: 90 units