Author Topic: 1960 Corvette front brake caliper nut  (Read 655 times)

Offline HerrOtto

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1960 Corvette front brake caliper nut
« on: August 26, 2023, 09:54:41 AM »
Hello, I need a front brake, rear of the caliper, nut . It is for a 1960 Corvette. It is fine thread, larger than 1/4" and metric M7, smaller than 5/16 and metric M8. The pitch appears to be metric 1.0.  I believe the caliper is original. I have tried the nuts from other older Schwinn approved calipers with no success. Does anyone know what size I am looking for?
Thank you

Offline HerrOtto

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Re: 1960 Corvette front brake caliper nut
« Reply #1 on: August 27, 2023, 08:39:37 AM »
I have gone to 2 local bike shops and a home center, with no success.  It is a strange size.

Offline Wayne

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Re: 1960 Corvette front brake caliper nut
« Reply #2 on: August 27, 2023, 12:50:04 PM »
Bike threaded hardware, ha! Bikes have been around before automobiles and many bike companies created their own hardware. Some examples, in Great Britain they had Whitworth thread (3/8" and larger) and Associated thread (smaller than 3/8"). French companies had their own metric threads. When Europe went to the Unified Metric system, many companies still used the tooling they had.

So, hard to read in your photo, it looks like the caliper was made in Switzerland. I know Whitworth and Associated threads are different than most as they have rounded thread tops, not sharp points like American standard threads or Unified Metric. I do not know if Switzerland used Associated threads, but with the rounded thread tops, smaller than 3/8", they look like Associated threads.

Offline acg_schwinn

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Re: 1960 Corvette front brake caliper nut
« Reply #3 on: August 27, 2023, 02:51:13 PM »
So, hard to read in your photo, it looks like the caliper was made in Switzerland.

I enlarged that on a big monitor and it is indeed "Switzerland," the second line of the stamping visible in Photo 2.

I know Whitworth and Associated threads are different than most as they have rounded thread tops, not sharp points like American standard threads or Unified Metric. I do not know if Switzerland used Associated threads, but with the rounded thread tops, smaller than 3/8", they look like Associated threads.

My go-to source for weird hardware bits is usually our local (and rather big) Ace Hardware store, where they have a huge aisle of nothing but nuts and bolts in all different types. In addition to the big bins of standard pieces, they also have dozens of plastic pull-out drawers full of specialty parts, really obscure stuff, so I would say it might be worth a try there if you have an Ace nearby.

However, if it's not a thread that's been in production this century, you are probably going to strike out with retailers. (I was not successful finding a modern supplier for the strange M5 thread pitch used by Huret on their derailleurs and speedometer mounting brackets.) Your best bet may be to find a used example from one of the Schwinn Bike Forum members rummaging around in their basement parts boxes.  :)

Offline Wayne

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Re: 1960 Corvette front brake caliper nut
« Reply #4 on: August 27, 2023, 03:09:07 PM »
I found it, Swiss Thury thread, with rounded thread tops like Whitworth:

From Wikipedia, the free encyclopedia
The Swiss-designed Thury screw thread (alternatively called the Filière Suisse, FS, screw thread) is a metric thread standard that was developed in the late nineteenth century for screws used in scientific and horological instruments. The thread is named after Marc Thury, an engineer and professor at the University of Geneva who contributed heavily to the standard's development.[1]

History
Development of the Thury thread began in 1876, when the Horological Section of Geneva Society of Arts appointed a committee to look into the requirements for a uniform thread standard for use in Horological arts in Switzerland.[2] Professor Thury began his studies by collecting and measuring samples of screws made by nine independent screw and screw tackle manufacturers in Switzerland.[3] The Thury thread form was developed in 1878, thirty-seven years after the British Standard Whitworth thread form was designed in England and fourteen years after the United States Standard thread was presented in the United States. However, unlike these two predecessors, the Thury thread was designed for small-diameter screws which were then produced with screw plates. This production technique mandated that the Thury thread form have rounded crests and roots.[4] Thread forms with rounded or "radiused" crests and roots like the Thury and Whitworth thread generate smaller stress risers than those forms like the American National or ISO metric which have truncated roots and crests; in modern engineering this is particularly important factor when tapping holes in acrylic plastic, where a larger stress riser can lead to an earlier onset of crack formation.[5] The Thury thread is unusual in having a comparatively small 47.5° thread flank angle,[6] which was chosen to make fabrication easier and to achieve greater holding capacity than screws with larger flank angles.[7] Screws in the Thury thread system are given nominal sizes, with the base size "0" being six millimeters in diameter and having a thread pitch of one millimeter. Sizes are proportional, so a size "1" is ten percent smaller in diameter that a size "0", while a size -1 is ten percent larger than a size "0". The Thury thread was believed to be the first thread form to solve the problem of creating a single system of screw dimensions applicable to all sizes.[8] The relationship between the pitch P of a Thury screw and its diameter D is expressed by the equation D = 6P5/6. Another variable Thury standardized is the thread depth, which had until then been variable when cutting threads in different materials.[9] The proliferation of the Thury standard was hindered when in 1882, the British Science Association produced a committee report on the consideration of a standard screw gauge, where they declined to accept the Thury thread but instead chose to use the Whitworth thread standard previously designed by committee member Joseph Whitworth, in part because the Whitworth form was historically successful and because the committee did not believe England was prepared to use a metric thread as its standard.[10] However, the committee recognized the validity of many of the design aspects of the Thury thread, and a mere two years later published their specifications for the British Association (BA) thread. The BA committee made only slight modifications to the rounding radii of Thury thread and gave specifications rounded to the nearest thousandth of an inch.[11]

Obsolescence
Despite being popular screw standards for nearly a century,[12] both the Thury thread and the BA thread have largely been replaced by the ISO Metric thread form. Today the Thury thread is rare outside of antiques due to the relative abundance of other standard sized fasteners. For example, the British Association 0BA, the Löwenherz 6 mm and ISO M6×1.0 fasteners have identical pitch and diameter to the Thury size 0 (however, they are not interchangeable because they differ in thread geometry)

Offline HerrOtto

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Re: 1960 Corvette front brake caliper nut
« Reply #5 on: August 27, 2023, 05:09:23 PM »
Success. 3 bikes shops and one home center later, Ace Hardware did indeed have the correct one. It is the seldom used or found, Metric M7 1.00 fine pitch.
I would never have found it on my own without the help of an elderly gentleman employee. You would have thought that M7 would be found right in between the M6 and M8 nuts, but that was not the case. Thank you all for your help.

Offline acg_schwinn

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Re: 1960 Corvette front brake caliper nut
« Reply #6 on: August 27, 2023, 05:50:27 PM »
Success. 3 bikes shops and one home center later, Ace Hardware did indeed have the correct one.

Congratulations! Back when I was in Tech Support, it was considered good form to not sound amazed when one of your suggestions to the customer actually worked ;), but I have to admit that I was kind of pessimistic about your chances of finding that nut at Ace, given what Wayne uncovered about its likely specs, so that's great news.