The humble file handle--it's always there when you need it. Here are a few I've accumulated over the years. These are all vintage, just some are of a more recent vintage: Lutz File & Tool Co. long-ferrule: Lutz seems to dominate the industry still. Best I can tell, they began in Cincinnati...
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I've never felt a file handle so expensive that it's worth possibly ruining the heat treat of any tool I want to rework to save the handle's cost.
The tang of a file is not heat-treated. Besides, it doesn't take red-hot to melt plastic.
I've been known to use anything at hand--a stick, cork, corncob... whatever. Especially for chainsaw files in the field.
But I'm always keeping my eye open for cool, old, purpose-made file handles at yard sales and junk stores.
BTW--for those not "in the know"--the proper way to seat a file in a wood handle is to place the file tang into the hole, then drop the handle end against the bench a time or two with the file sticking straight up. Let the weight of the file do the work. To remove one, I open the jaws of a vise enough to let the file through but catch the handle, then drop the file into the vise jaws. The file usually pops out of the handle on the first try. B sure to catch the file.