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It turns out that the use of left-handed thread is not as uncommon as I once thought. Unfortunately, finding replacement left-handed nuts, bolts and screws isn't easy.

A while back, I damaged the thread on a left-handed nut that was meant to secure a radiator fan on my Chevy. The nut was unusable. No mechanic or dealer had a replacement in stock.

I had to get creative in order to reinstall the fan, so I cut regular right-handed thread onto the fan motor shaft with a die, dabbed on some red Loctite, secured the fan with a regular nut and called it a day.

For a part as simple as a nut, it makes little economic sense to purchase a specialist tap-and-die set designed to cut left-handed thread. It doesn't help that any left-handed fastener is extremely difficult to source.

So what other tricks or workarounds could a person without access to a specialist tap-and-die set utilize in order to overcome the absence of left-handed fasteners?

  • Thread files have been very useful in the the past. – vini_i Feb 27 '16 at 22:59
  • @vini_i saved by those many times...and just using thin regular files to clean some threads up but....never have I done this before. +1 for a snowflake of a question. – DucatiKiller Feb 28 '16 at 0:31
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There is a tool known as a thread file. While it is a semi specialty tool, it is common for garages to own one.

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A thread file only depends on the thread pitch and independent of both the diameter of the fastener and whether it is left hand or right hand thread.

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On the ends the tool also includes files meant for internal threads. There is a size limit to the diameter of the internal threads that can be repaired.

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The specific repair you describe; repairing a radiator fan without the correct fixings, can be done in a number of ways.

One of the most creative ways I've ever encountered was on La Carrera Caledonia Rally of 2006 (in which I competed as navigator in this glorious Lancia Flavia Coupe) one on the competitors encountered a problem out of the road that the radiator fan coupling had failed on his rear engined competition car and he had only limited tools available. He hunted around the car and managed to find a welding rod. He then used jump leads in liue of welding gear and managed to get a tack weld which actually held for the remainder of the event. He did not win the rally but did win a prize at the evening dinner for most ingenious repair.

There are any number of ways to effect a repair when you don't have the correct fixing. These typically include zip ties, rivets, duck tape, bits of wire, the "wrong" nuts and bolts packed with lots of washers. It very much depends on the situation you find yourself in and what you have to hand. Some repairs will be more appropriate (i.e. last longer) than others. In a fully equipped workshop, I'd have probably opted for something similar to what you did.

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Left handed nuts are typically cut that way so the spinning of the motor/engine will not loosen the nut over time. A right handed nut will likely loosen over time from the torque of the motor starting. If you use a castle nut with a cotter pin, it should stop the nut from removing itself.

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