1.375 X 24, ISO 6696 thread standard, 2008

[spinningmagnets]

There was a recent discussion about a thread that is often found on freewheels and bottom-brackets. Staton-inc/Sick-Bike-Parts-SBP make shaft adapters to attach a freewheel to various diameters of shaft, and this thread is also used in freewheeling cranksets, and the creative non-hub community is using this thread in several different ways. The info supplied is important. I will copy-paste the start of that discussion here, so it can become an easy-to-find reference. http://endless-sphere.com/forums/viewtopic.php?f=28&t=42785&start=2600#p805687

LightningRods:

Has anyone actually used ACS-Crossfire freewheels and White Industries freewheels interchangeably? The ACS is listed as a 1.375" -24 tpi thread and the W-I as a 1.37" -24 tpi thread. Trials cranks are typically 1.37" thread and the BikeMotive cranks are 1.375". The GNG seems to be 1.375" with a metric thread per mm. I've read about Forum members stripping their crank threads all the time. Mixing and mismatching these thread sizes and pitches will do that. I need to confirm with Cyclone what their crank thread is. They offer a heavy duty five bolt freewheel but I would rather use ACS or W-I if I could.

Denisesewa:

I have used the ACS claws and the white and the GT 120 point freewheels on my trials cranks, I can see or feel no differance, I have a GT on my GNG cranks right now and it went on without issue, however it did not want to screw on easily to the GNG jackshaft pulley adapter, I attributed this to poor machine work ( perhaps not? ) , I think its easy to start these fine threads cross-threaded and that leads to people having trouble, also of note is all my trials cranks are " high end" which means they are probably machined to closer tolerances, however I just tried the GT, ACS claws and the original GNG freewheels on a set of cheap cranks from "Sick Bike Parts" and they all spin right on, Both whites I own are on trials bikes right now, sorry, not going to tear my bike down to test, but I know the whites are the same. ALWAYS use Never-seize! (http://www.bostik-us.com/our-brands/never-seez)

E-Norco

The Try-All cranks I use are 1.37" x 24 TPI
( http://www.tartybikes.co.uk/cranks_pair/tryall_expert_isis/c514p11216.html )

The stock GNG freewheel (1.375") was difficult to fit and I think my thread is affected now.
I never thought about different thread sizes till now .
The ACS I planned to use is 1.375". ( http://eclipsebikes.com/crossfire-freewheel-p-1075.html )
The Dicta is 1.37" ( http://eclipsebikes.com/dicta-freewheel-p-1039.html )
What thread size is the stock big belt pulley adapter

LightningRods

Thanks everyone for your replies. I'm not sure that I'm any less confused but I do have a few more options now.

On the Gen 1.0 that I bought: the crank arm thread, the BB-cup thread and the big pulley adapter are all the same. As I said I believe it to be 1.375" x a metric thread. The Chinese mix and match US and metric sizes depending on where they 'borrow' their tech from. I bought a pulley with a cheap four bolt Chinese freewheel on it and it also threaded into all of the various GNG parts.

I'm going to offer my 90-tooth GT2 pulley with and without freewheel. All of the pulleys will have a 3.07" flange mount in the center. I'm going to have my machinist Steve make freewheel to 12mm threaded adapters and 3.07" to 12mm shaft adapters for those who don't want to switch over the freewheel. I need to decide on a thread size for the threaded adapter. I think I'm going with 1.375" x 24 tpi. It's a standard 1 3/8" die instead of some odd duck proprietary -.005" size that the trials bike parts manufacturers dreamt up. They must think they're plumbers. :wink:

On the BB I'm going to offer both four bolt and five bolt 219 sprocket adapter plates so you can fit whatever type of freewheel will fit your crank arm. I can't possibly know all of the many crank arm thread sizes but I would expect most quality trials parts to be 1.37" which is White-Ind compatible, not Chinese four bolt or ACS five-bolt compatible...Bikes are simple, right???

speedmd

To my knowledge, the 1.37 and the 1.375 are identical pitch diameter threads and have been for some time. Difference being the tips of the threads are shortened/flattened .005 to allow more wall / less stress concentration on the female side on thin-walled BB components. As long as the male threads don't come to a sharp point, there should be no issues anywhere on interchangeability. The stock GNG crank-arms were a poor example of suitable thread quality on my set, but were very snug, and so much better than being loose in my book.

Denisesewa

Thanks for that, kinda explains why I havn't had an issue with any of my trials stuff.

E-Norco

In the description from the ENO it seem to be different sizes ["...Uses 1.375" x 24 tpi thread. Please note that this is slightly larger than standard 1.37" and we recommend at least 9 threads of contact between crank arm and freewheel to prevent the crank arm thread from being stripped..."]
http://www.tartybikes.co.uk/complete_freewheels/white_industries_eno_trials/c16p77.html

speedmd

What I understand is that in the 2008 time frame the former "compromise" thread 1.37x24 standard was abandoned. It was essentially replaced by the 1.375 X 24 ISO 6696 standard. The pitch diameter standards and gauge limits are specified in much greater depth in the new standard and are virtually identical. Remember 1.37 or 1.375 is the overall diameter and not the critical pitch diameter, and we are talking roughly .002" per side on a theoretical tip of thread (male) and root of thread (female) side of which there was a great tolerance to begin with. There should be no interchangeability issues between them. That being said, I would never suggest that every thing out there meets acceptable quality standards. Too many years in the quality business to take anything like this for granted

LightningRods

Here is a direct warning from Trialtech regarding exactly this issue:

"Please note that the minimum required thread contact between crank arm and sprocket/freewheel is 7mm, and a 1.37" sprocket/freewheel with maximum internal thread diameter 33.80mm (NOT 1.375") must be used. Failure to adhere to this instruction will damage the cranks threads and this is not covered under warranty."

I bought both a flanged ACS 1.375" and 16 tooth ACS 1.375" and neither of them fit the GNG pedal crank or freewheel to 12mm shaft adapter. A mechanic friend of mine made the same comment about the thread peaks causing interference so I filed them down. The ACS freewheels still would not thread on past a couple of threads. The diameter fit feels loose after filing. It's the threads that bind up eventually.

I don't claim to have the answer but I don't think we have an answer here yet.

Denisesewa

I think trying things on the GNG components will not supply the answer as I am convinced their machine work and QC [quality control] is terrible, both of my kits have shown differences. I think you are going to have to pick some components that "do" match and build your stuff around them, most of the GNG stuff isn't worth keeping if you are upgrading anyway, and those who are interested in your parts should be willing to pay the difference.

speedmd

Easy enough to measure the pitch diameter of the external threads with three wires and a micrometer if your good with them. Willing to bet you will see that the pitch diameter is way off (big) on the GNG threaded arms. Machinery's handbook has this inspection process in detail. Forget measuring the inside threads. Plug gauges used for that. Not sure where the 33.8mm/1.331" comes into the picture unless they are calling this "internal thread diameter" instead of what has been universally accepted as the "minor diameter". The ISO 6696 has the latest breakdown but can tell you from experience that they are typically not worth buying these ISO specs unless your making taps / dies or gauges. My opinion is that if the spec is kept from the public, it is relatively worthless to use as a reference. They have created there own little monopoly

speedmd

It looks like the trials crank folks are still using the old standard and going overboard on the mating parts spec. Park tools has listed the female minor diameter tolerance of the 1.37 x 24 threads at 33.6 -33.9 mm or 1.3228 -1.3346" If they require something tighter than the spec (33.8 max), it must be a borderline situation strength-wise, the way they cut the threads or due to the added torque of the little freewheels/ long crank arms and a big aggressive rider hopping on it, that they fail quite often. They would be much better off cutting the crank threads the newer slightly larger 1.375 size than sorting through freewheels for a tight fit...Just a thought.

Looks like good quality steel wire .035 -.036" diameter would work well to gauge pitch diameter well for this size external thread so you can see what your up against on the cranks from the east.

1-3/8x24 is 1.3466- 1.3423 pitch diameter. Internal minor diameter is 1.330 -1.340. If you don't' have a handbook let me know and I will look up the correct wire sizes for you.

LightningRods

It appears that 1.370" is standard English and Italian BB thread. It's referred to as "35mm" but the spec is 34.6-34.9mm OD. 1.375" equates to US 1 3/8". It's MUCH easier to get taps and dies for 1.375". I've written ACS and White Industries asking for their take on this. I'll let you know what I find out.

speedmd

The 1.375x24 is the new ISO standard. I would not waste time with the old ones. 1.37 was a compromise bicycle thread to begin with, not a UNF and anyone still making stuff to that standard is just asking for trouble. Here is some more on measuring the male thread. You will need a 2" micrometer and three sections of identical size wire/ drill bits (shanks). Mine is tightly assembled and I don't have the freewheel tool or I would measure it. Will worry about taking it apart when it dies. If you have a set of arms free, let us know what you get for Pitch Diameter.
Good write up on this by Thun.
http://www.thun.de/fileadmin/user_upload/documents/Glossar/Assembly_gb.pdf

Sheldon Brown has some on it also.
http://www.osbornproducts.com/three_wire_method_measuring_pitch_diameter.htm

http://dc308.4shared.com/doc/KyDHhvij/preview.html

 

[E-Norco]

White Industries Website:
http://www.whiteind.com/free-wheels.html

Information from Tartybikes http://www.tartybikes.co.uk/complete_freewheels/white_industries_eno_trials/c16p77.html
Description:
"- Uses 1.375" x 24 tpi thread. Please note that this is slightly larger than standard 1.37" and we recommend at least 9 threads of contact between crank arm and freewheel to prevent the crank arm thread from being stripped."
Additional Information
" Can be used on the rear as long as you have a hub with standard 1.37" x 24 tpi thread and the freewheel's thickness will clear the dropout of your frame."

This is very confusing

 

[LightningRods]

More on the 1.37" vs. 1.375" saga. I wrote to ACS, White Industries, BikeMotive (they have a BB freewheel kit using the ACS) and Sick Bike Parts that sells the W-I HD flanged freewheel.

Sick Bike Parts: "That is what size it is [1.375"], we just left the .005 off."

Bike Motive: "Great questions. The 1.37 & 1.375 are the same, with the former spec showing less precision, probably just as a shorthand. Yes the White freewheels fit great, as does every other brand we've tried."

This backs up what Denisewa and SpeedMD said and makes it seem like Trialtech was taking something they didn't understand much too seriously. If I hear similar stories from W-I and ACS I'll just order parts and stop thinking about it.

I was hoping to be able to do partial upgrades on the GNG BB for people on a budget but it's looking pretty hopeless. Everyone else's parts interchange just fine but the GNG crank arm threads are too sloppy to thread a standard freewheel onto without stripping. I'm buying some of the Cyclone ISIS crank sets. I hope their QC is better GNG's. For people using their GNGs on the street or for light off road BikeMotive has a square taper spindle kit similar to the GNG only well made.

My thanks to all of the generous, knowledgeable and helpful people on this forum.

 

[speedmd]

A good post at the end of this thread.

http://forum.slowtwitch.com/cgi-bin/gforum.cgi?do=post_view_printable;post=289691;

 

[spinningmagnets]

from ES member LightningRods:

More on the freewheel thread compatibility issue:

I just ordered a crate of Cyclone ISIS BB cranksets to use on my upcoming complete kit. The threads on the Cyclone crank arms are compatible with the 1.375"-24tpi standard freewheel thread. The flanged ACS I have threaded right on with no interference. The Cyclone set ships with a five bolt Dicta freewheel. I also bought 10 extra heavy duty freewheels from Cyclone that look suspiciously identical to the ACS.

The 16 tooth freewheel that comes with the GNG will not fully thread onto the Cyclone arm. I bought a pulley some time back that had a cheap Chinese 4 bolt freewheel that fits the GNG crank arm and freewheel hub adapter on the jackshaft. It doesn't fit the Cyclone crank arm.

I just put the GNG and Cyclone crank arms side by side and scanned them. The Cyclone threads are exactly 24 threads per inch. The GNG threads are just over 25 threads per inch which comes out to 1.0 thread per mm, a standard metric thread pitch. I flipped the image of the Cyclone threads over the bottom of the GNG so you can see the mismatch.