It's a leftover from the days when I used to race dirt bikes, and had to loosen steel Phillips-head screws from aluminum transmission cases. I only use it maybe twice or three times a year now, but when I need it, I'm glad I've got it.
I'm talking about an impact screwdriver. It''s a sturdy steel cylinder with a cam device inside. You put a screwdriver bit in one end and press the screwdriver bit against a stubborn Phillips-type or slotted screw head, and smack the other end with a hammer. The cam inside the metal handle translates the downward movement of the hammer stroke into circular motion. The downward impact forcing the screwdriver bit into the screw head, combined with the simultaneous rotation of the bit, can magically loosen stubborn, frozen screws.
Impact screwdrivers worked great on motorcycle case screws because they were usually frozen by galvanic corrosion. Once they were broken loose, they usually turned out easily. Impact screwdrivers can remove rusted screws that resist removal until the final thread clears the hole, but it takes patience and a lot of pounding.
A replacement impact screwdriver with a set of Phillips- and slotted-head screwdriver bits would cost me between $25 and $90, depending on how fancy and sturdy of a kit I buy. If I break or lose this tool that I only use once, maybe twice a year, could I justify spending the money to buy another one...?
Yep. I'd probably grumble about it, but those few times I've used my impact screwdriver in recent years have been lifesavers. It's one of those tools that you rarely use, but really need when you need it.
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