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How to Repair Threads With a Thread File

The Thread File: A Money-Saving Tool

In the process of the “custovation*” of a well used — and possibly abused — motorcycle, you’ll eventually be dealing with threaded hardware replacement.

More often than not the decision will be what kind of hardware to select to replace the rusty and buggered fasteners that are holding the parts together.

With typically-sized bolts from small to medium sized diameters, the custovator has a choice of threads to repair.

These can include SAE, Metric and the always perplexing Whitworth types to match the project’s country of origin.

Their availability is widespread and even the more exotic threads can be acquired from hardware specialists.

But what about the “plus-sized” hardware?

You know — the ones that were machined at the factory, they take the biggest spanner in your toolbox, or bigger yet, a grande size crescent wrench to grab the flats.

Threads Needing Help

Think about external threads on axles, the steering head shaft, shock bolts and the like. Or on the older BMWs, the 1-1/4 inch diameter metric threaded alloy exhaust header nut.

Repairing external buggered threads on these parts means either total replacement or machine shop time. Both solutions are very expensive.

I ran into the buggered thread problem a number of times and always had that cold chill of unexpected expense run through my pocketbook.

I prefer to spend custovation bucks on parts that pay off in appearance or reliability rather than fixing damage that some careless bloke inflicted on the unsuspecting machine.

Thread types

To the Rescue

The rescue mission is handled by the little known thread file. The guy who invented it should be enshrined in the Custovator’s Hall of Fame, with a forever-burning votive candle standing guard!

The thread file is a simple hardened steel four-sided bar with 8 different thread sizes cut into the body. It’s available for all thread patterns — even Whitworth.

The thread sizes are stamped on the sides for confirmation.

Easy to Use

If you are not sure of the thread size, match up the bolt thread to one of the file sides.

Some of the thread sizes may appear similar, so I double-check with the file firmly engaged with the section of good threads placed in front of a bright light to highlight that the file is correct for the thread.

If the file side is incorrect, light will show through the incorrect thread engagement.

Incorrect fit for thread file Correct fit for thread file
Left: Incorrect fit. Right: Correct fit.

Once you’re convinced that you have the correct side, gently stoke the threads just like doing a finish filing job on a piece of metal.

Not too hard and not too soft. Don’t worry about cutting too deep or flattening the cylindrical bolt shape, the file limits the cut depth.

Sometimes the buggers are isolated deep nicks.

Other times it’s a damaged section that’s been chaffed by another piece of metal.

Start with the good section of thread just next to the buggered part and start filing around the bolt toward the known bad section.

After one file pass, spritz some WD-40 and try the nut for smooth spin-on.

If it binds don’t force it — make another pass instead.

Do that until the nut spins on easily. Continue with the file and spin technique; notice that the bad section gets shorter leaving the worst section as the last to be finished.

R65 exhaust collar R65 exhaust collar repaired
BMW R65 exhaust collar repair.


On the BMW, a $15 metric thread file saved over $600 dollars worth of head replacement or an alternative $300 machine shop bill.

On other dirt and street bikes the savings was priceless. Outfitting your tool box with a SAE, Metric and Whitworth thread file set will be less than $75.

And guess what?  Having that Whitworth file may be just the right excuse for buying that needy vintage British bike you saw on eBay.

The thread file



Custovation is a combination of customizing, and renovation, not a restoration, which means to bring back to an original condition.

Custovation has a more specific meaning: CUSTOMIZE — to make or alter to individual or personal specifications, combined with RENOVATION — which is to restore to an earlier condition, by repairing or remodeling.

Publication Date: November 2007

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From “J.D.” (July 2014): “I did a Google search on “how to you use a thread file” and your write up was the first listing. I was in need of a 12 x 1.25 “thread chaser” but couldn’t find one anywhere. This kit was the only way I was going to get one quickly.

Thanks for a great article! Last night I purchased the Craftsman Master Thread Restorer Kit (Part number 52105) and was perplexed when I saw these files in with the rethreading taps and dies. Thanks to you, I now know what I’m looking at and how to use it.”

From “A.D.” (February 2014): “Very nice write up, I was afraid to use the thread file, I thought it was going to be a whole big thing, but your write up simplified it for me. Thank you.”

From “M.M.” (1/09): “I’m writing to second your endorsement of these tools – they’re AWESOME!  I worked on bikes for 15 years before I found them. Everyone who works on machines of any type NEEDS these in their toolbox. They are truly lifesavers.”

From “S. McD.”: “Hey guys, great article. Just wanted to note as an additional and frequently much less expensive option, this (Craftsman 48 pc. SAE & Metric Thread Restorer Kit; Sears item # 00942275000) kit from Craftsman.

AAt 60 bucks (often less) it’s a great deal and has saved my bacon a number of times. I have found it invaluable for cleaning up the threads on Showa and KYB shock shafts when doing rebuilds.

Depending on the model, you have to carefully grind off the nut that retains the valving, and most of the time this will ding the threads up a bit. One of these files is the perfect solution for this type or similar work, as you’ve noted.”

Editor’s Note: I have one of these kits also and you’re so right, it has saved me several times!

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