AK Model 42 Transformer Ground?

[Winky Dink]

Possibly it's a dipping thread. The second transformer I looked at has one on top and one on the bottom, and they're long enough for that purpose. I don't think Atwater Kent would have needed to varnish the outside since they were entombed in sealer, but I don't know if Atwater Kent made the transformers or if they came from a different manufacturer.