I have an early rear brake caliper adjuster that was seized on the adjuster screw. I got it off but there is now a slight amount of roughness toward the end of the the travel when screwing the parts together. It's probably fine but I'm thinking the smoother these operate, the better and I feel better if I could just clean it up a bit. Problem is they are M7x1.75 threads and finding a tap of any kind this size appears impossible. What other options are available to clean up the female threads?

You can use a chase instead of a tap to clean threads. you can make one by cutting a lengthwise groove in a proper size bolt.

"Taps and dies allow you to create threads. Taps are male cutting tools that create threads in a female hole. ... Instead, use a “forming” or “chaser” tap that is specifically designed to chase and re-form the existing threads instead of cutting thread material away."

Thanks Mark,
The problem is these are really weird threads. I can't even find a bolt this size, let alone a tap, let alone a chaser tap. I just spent the last hour googling. Any M7 fastener is kind of rare and these are super coarse threads to make the helical adjuster mechanism.

find a machinist and have them chuck it up and clean up the threads. You can make any pitch at any diameter you want on a lathe.

Cool! I'll do that. I wondered if a machinist would have any tricks that would work. Thanks!

You can get a metric thread file

I have a set of jewelers files that I've used to clean up threads, it's not fast but they work on any thread and pitch. You just have to go slow and pay attention.

Tim

After soaking the parts in mineral spirits and running the adjuster screw through the hub several times, the problem seems to be fixed and it is running silky smooth. I must have dissolved off the rust.

But I'd still like to learn from this about repairing threads as it's a common problem we all face. I've never used thread chasing files but everything I've read shows them being used on external threads. Can they be used on internal threads? Same question for jeweler's files? These files look like something that would be handy to add to the toolbox but they are only good if I know how to use them.

Thread chasers are worth their weight in gold. And the files are also very nice. I just chuck them in a lathe and go to town unless it is something you can't get into a lathe easily.

Glad it worked out, I doubt you dissolved the rust, but you might have gotten rid of the gunk that contained some iron oxide.

KD tool # 2228

The other numbers you see are thread pitch. This is the shizzle if you can’t use a die

Gear Wrench also makes one and it is on prime, GearWrench 2228D External Thread Restorer File Metric.75, 1.00, 1.25, 1.50, 1.75, 2.00, 2.50, 3.00 Pitch, Black

Thanks guys. I'm going to buy one of these files. What about internal threads? I'm guessing options are more limited there.

A tap. On occasion I've had to buy an individual tap and modify it to work (grind the tip off).

Thanks Perry. And that was my original problem that a tap for this weird size/pitch combo wasn't available.

BTW, earlier when I said the soak in mineral spirits might have "dissolved" some rust, I should have said "loosened." I agree it wouldn't have dissolved any, but I think it softened stuff up enough that the screw was able to finally knock it out. Good thing since these adjusters are NLA and hard to find without buying a whole caliper core!