Um, a lightning arrester for parallel open-wire transmission line? Clamp a pointy nail in each side, ground the center block and pass each side of the feedline under the lower thumbscrew on each side? Slide each side block to get the desire gap from each pointy end to the center.
Just guessing, mind you.
Does bring to mind my grandfather's tales about ham radio on the farm in the 1920s. A ham antenna was the longest wire you could string. Said he had one a quarter mile long. Until a thunderstorm. A lightning stroke left him with about twelve feet of charred wire, total. A lighting arrestor would stop the surge you get from a neighbor's tree getting struck, but not from direct hit.
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