Unusual Thread Size

[lilcraigford]

I’ve run into a thread size that I’d like to bounce off of the knowledge base that is Garage Journal. I think I have the thread size figured out, but its so uncommon that I’d like to see if anyone recognizes it as a thread from some other standard. Moving on…

Based on measurements with a dial caliper and a metric thread pitch gauge, I believe M48 x 0.75 is the thread size in question. The application is a set of automotive coilover dampers and the parts are male gland nuts and their respective housings. I second-guess my conclusion because I can’t seem to find this thread size anywhere. It doesn’t appear in any of my go-to resources. The tables in the the Machinery’s Handbook and websites such as Maryland Metric or Engineers Edge list 1.5mm as the finest pitch for a 48mm thread diameter. The only place where it has turned up in internet searches (that I’ve found) is with the astronomy crowd. They use M48 x 0.75 for mounting various adapters and accessories. Maybe this is a case where the company which produced the coilovers wanted something “proprietary”. Unfortunately said company has been out of business for 5-6 years now, otherwise I would direct my inquiry to them. Let’s look at some numbers…

- Possible Thread Size: M48 x 0.75

- Measured Major Diameter: 1.887” (converts to 47.9298mm)
- Measured Pitch: 0.75mm

Out of curiosity I converted from metric to inch, then converted the closest inch size back to metric.

- Converting metric to inch: M48 x 0.75 = 1.88976” x 33.866 TPI

The closest inch size would be 1 7/8"-34, which seems less likely than M48 x 0.75.

- Converting inch to metric: 1.875” x 34 TPI = M47.625 x 0.747

 

[PETE14]

My opinion? You have carefully measured it and correctly determined what it is.

Funky odd ball threads are definitely out there. The company I work for manufacturers medical machines. There is a nut we use that is something like 2 inches in diameter with a thread pitch of 32 TPI. Very fine thread for its size. It uses a totally custom socket with a bunch of pins sticking out to tighten it. Some engineer decided thats what he wanted so there it is. Odd ball stuff is out there.

 

[pi_guy]

Who is the manufacturer?
My close friend builds custom shocks and is a Penske shock dealer.
Quite often if there is a good product no longer made somebody might be producing parts for it.

 

[Millwrong]

Fasteners will typically use a standard thread form and size. When you start getting into machinery and other manufactured products, all bets are off. You'll typically find a standard pitch, but don't expect it match up with a "standard" size.

 

[larry_g]

Fasteners will typically use a standard thread form and size. When you start getting into machinery and other manufactured products, all bets are off. You'll typically find a standard pitch, but don't expect it match up with a "standard" size.

There are SAE standards, and many others. The automobile industry established many of the standards we use today, but this in no way dictates what must be used elsewhere.

lg
no neat sig line

 

[matt_i]

I looked into bearing locknuts which are typically large diameter small pitch, but the diameter steps are in 5mm increments, 40, 45, 50. And 1.5mm pitch. So no help there.

I think you are going to have to make an M48 x 0.75 nut and try it out for fit. Hopefully you have access to a lathe that can chase the metric pitch.