Vac-o-matic is correct ... that is an early Belden cord and, yes, the ones they made for the Kirby 505 had matching - but larger - female plugs for the motor end.
I don't know when they changed the male end to the type that we think of as the "classic" Belden plug [see ad below] but I'm guessing later 1940s as all the Lux XXXs I've seen had Belden plugs with the newer plug. Belden's later Kirby cords had flat male plugs with the Kirby logo on them.
Hans, you didn't tell the best part about this Filtex -- who it belonged to before I had it! It was Stan Kann's! He gave it to me quite a few years ago. He never was thrilled with it because, to him, "it's a noisy thing!" I dropped enough hints about how fabulous it was and finally one day he said, "Well, go ahead, take it home since you like it so much."
I have other machines that Stan gave me, so I thought it would be nice to give this Filtex to Hans. And I have two other Filtexes, one just like it and one that I think is a little earlier because the logo treatment is different. It's the one the left-most side of the photo below.
The hose you made for it looks nice - the original is black with silver "dotted" stripes. See photo.
