This could be used for many things, but it was designed for supporting old plaster ceilings when repairing them. You use a long drywall screw through this into a rafter, to gently raise sagging plaster after injecting repair glue through holes. Search on YouTube for more information on how to do this. 

The hole in this washer is contoured to fit a standard drywall screw so it should not create too much stress on the washer. You can reuse this many times.