Need help here guys. We're all lost on this one. Where did the terms FS and FD come from?

Ferrous shallow and ferrous deep.

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Charlie Eldridge, Indianapolis, Utility Power Guy

And FB is Ferris Buehler.

And you need a day off Ryan!

Tell me about it! In fact, I think I'm getting a cold....

Ferrous?? Sounds like my students ... I had one who absolutely could not understand why his magnetic level would not stick to the box. (this was a high school junior)

Ahh, another example of a term gone whacko.

I always heard the same as Charlie.

So, now, lets all go put in our PVC or Aluminum Fs Boxes !!
And FW is Ferris Wheel.

Everyone knows that PVC means.......
pipe very crowded!