The clips on each of these have a "K" on the clip, all right. Duh. It could be Keystone, but could it also stand for Kahn?
That’s as far as I got with that line of thought. In the meantime, I found this example of a Keystone, which to me answers the question:
Here’s the clip and band close up:
I don’t believe the Keystone was a Kahn brand anymore, and I think I know whose brand it was:
That’s the Keystone next to a Stratford, made by Salz Bros. (in the later years of the company, Salz dropped its old name and simply went by "Stratford").
These two couldn’t be any more alike: