How to make a "good" copper tubing clamp

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Original poster: "McCauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com> 

Just curious if anyone had a good way to make a wire clamp that would
fit over refrigeration copper tubing (primary coil) of about 1/2" to
3/4" in diameter.

I've tried a variety of different ways, but am having trouble getting a
clamp that puts positive clamping force on the
copper tubing.

Any help appreciated.
Thanks

Dan