Fresh air box with bracket on bottom???

I am finally back on my project after very long hiatus waiting for my son to get interested. The forums have been very useful and I can find most answers without posting but I am at a loss now. I am in the process of fitting everything to finalize wiring harness. In doing so I am scavenging from the three heater boxes and fresh or boxes to make a complete good one. One of the fresh air boxes I have has this bracket fastened to the bottom. Is it factory or something a P.O. installed? If factory does anyone know what it is for? Thanks