Large Oring with new Powerfeed body?

[Destructo6]

I just took possession of a new, $20, steel powerfeed body. It arrived with the front screw + washer, powerfeed plug, and a large Oring wrapped around the powerfeed-body joint.

What purpose does the large Oring serve?

PS I could swear there was a post about this Oring not long ago, but couldn't find it.

Thanks.

[Enemy]

its just there to keep dirt out of the seem... the powerfeed is welded on on the top and bottem but not on the sides!!! you dont really need it but some people prefer to have it there i dont like it so i dont have it!