Wayne, thanks for the Unistrut tip. I have contacted them and they
will be shipping some samples to me. Have also discovered other
possible manufacturers/suppliers of spring nuts such as Haydon,
Cantruss, Hammond, and Tessco.

Regarding McMaster-Carr, I was unable to view their online catalog
because it requires a Java-enabled web browser. That is a no-no around
here.

Lyman