A Puzzlement

[Randy Ryan]

OK Boys, who can tell me what thread is used in the OS .35S? It measures 3mm but its NOT a .5 pitch.

[Steve Helmick]

Like a ST .46 or .60, they're 3mm x .6, so substitute 5-40 socket heads. The counterbores in the head still fit ok.  Steve

[john e. holliday]

I do not work for them, but go to your local Ace Hardware Store.    Hopefully yours will a department for machine screws of all types.   Take your engine with you and start trying the screws until you find one that works.   I do that a lot and the new clerks look at me funny when I lay the engine on the counter to pay for the screws.  I replace the stock screws with socket heads on all my engines.

[Randy Ryan]

Like a ST .46 or .60, they're 3mm x .6, so substitute 5-40 socket heads. The counterbores in the head still fit ok.  Steve

.6, that makes more sense, thanks Steve

[Steve Helmick]

Randy...I've never found a reference to 3mm x .6 threads here. My guess is that it was once a standard size, but is no longer. I've also read posts that said it was still available overseas, and that ST actually used 5-40's, but that just doesn't make any sense to me.

The bottom line is that 5-40's will solve your problem, and FWIW, the socket head ("Allen Screws") in 4-40 and 5-40 both use the same wrench size, 3/32", a good thing!  Steve

[Allan Perret]

Micro Fasteners had the 3m x .6 pitch about 4-5 years ago, I got a set of 10 for my 35S.   They may still have some, but you have to call to order them as they were not listed is their catalog.

[Randy Ryan]

Randy...I've never found a reference to 3mm x .6 threads here. My guess is that it was once a standard size, but is no longer. I've also read posts that said it was still available overseas, and that ST actually used 5-40's, but that just doesn't make any sense to me.

The bottom line is that 5-40's will solve your problem, and FWIW, the socket head ("Allen Screws") in 4-40 and 5-40 both use the same wrench size, 3/32", a good thing!  Steve

Yeah, the 40 pitch is off about .001 or so,  so the screw eventually binds in the thread. I'm going to try to locate .6's, I never did like bastardizing threads like that. This is customer job too, I don't want to "hack" it. 5-40s only as a last resort. Thanks everyone.

[Garf]

5-40 works fine for Super Tigre, NOT OS.

[Bill Hummel]

Most 35-s engines use the M3 x 0.6 thread.  Micro Fasteners does indeed still sell these, and lists them in their on-line catalog as metric socket head "M3 x 0.6 x 12mm". You just need to cut them down a bit for the back cover screws, or if they bottom out as head screws.

[Randy Ryan]

Most 35-s engines use the M3 x 0.6 thread.  Micro Fasteners does indeed still sell these, and lists them in their on-line catalog as metric socket head "M3 x 0.6 x 12mm". You just need to cut them down a bit for the back cover screws, or if they bottom out as head screws.

Thanks everyone, but I have to buy these in bulk, they're out there somewhere, I'll find them.

[pat king]

The M3 X .6 is the old JIS (Japanese Industrial Standard) 3 mm screw. The Japanese seem to have migrated to the ISO M3 X .5 screws. I know Enya has gone to the M3 X .5 in their newer engines. I don't know when the change occured, but all the old crossflow engines are M3 X .6, I haven't checked any of the new crossflow engines.

Pat

[Joe Just]

[quote author=john e. holliday new clerks look at me funny when I pay  

 Yea Doc! I believe that! Happens to all of us with stylish beards.
Joe

[wwwarbird]

Thanks everyone, but I have to buy these in bulk, they're out there somewhere, I'll find them.

 Good luck finding them anywhere else, please let us know if you do though.

 I just recently did this same search for .35S screws. I wanted allen heads to replace the worn phillips on three of my engines. They are in fact the M3X.6mm. I looked everywhere it seemed. The only place I was able to find the .6 was from Micro Fasteners in a 12mm length. They have them in 10 packs so the price wasn't too bad. The original ones are 10mm, but I doubt you'll find them. I just knocked mine down and finished them up with the Dremel and they worked perfectly.

[Randy Ryan]

Good luck finding them anywhere else, please let us know if you do though.

 I just recently did this same search for .35S screws. I wanted allen heads to replace the worn phillips on three of my engines. They are in fact the M3X.6mm. I looked everywhere it seemed. The only place I was able to find the .6 was from Micro Fasteners in a 12mm length. They have them in 10 packs so the price wasn't too bad. The original ones are 10mm, but I doubt you'll find them. I just knocked mine down and finished them up with the Dremel and they worked perfectly.

I hear you Wayne, but $4/10 is way too steep, I need at least 70 of them. I just send a note to Micro to see what kind of bulk price they might give me for 100 of them. We'll see.

[wwwarbird]

I hear you Wayne, but $4/10 is way too steep, I need at least 70 of them. I just send a note to Micro to see what kind of bulk price they might give me for 100 of them. We'll see.

 Building a radial?

[Randy Ryan]

Building a radial?

Unfortunately no, but if I were I'd be useing 4-40s!

[john e. holliday]

Hey Randy,  try RTL Fasteners for bulk machine screws.  He is a great person.   

[Randy Ryan]

Hey Randy,  try RTL Fasteners for bulk machine screws.  He is a great person.   

Thanks Doc, I'll check it out.

[Dallas Hanna]

The M3 X .6 is the old JIS (Japanese Industrial Standard) 3 mm screw. The Japanese seem to have migrated to the ISO M3 X .5 screws. I know Enya has gone to the M3 X .5 in their newer engines. I don't know when the change occured, but all the old crossflow engines are M3 X .6, I haven't checked any of the new crossflow engines.

Pat

Just to add a bit I wrote on the subject on SSW:

"Hi Steve. Actually the Japanese mimicked the Europeans or in reality, the Japanese adopted the European SI Metric for their JIS standard. That's why older European engines such as ST had the M3 x 0.6 threads. If we look at the ST wire type needles, they had the M2.3 x 0.4 pitch from the old SI standard as well. Think we'll find it's of French origin but also the DIN german standard according to the charts.

At $4 per 10 for a now special thread I wouldn't think it too expensive compared to some of our other modelling costs and habbits."

For ref, the ST engines from the 70s at least used American threads.  The ST 46 and ST 60 (Blue head 60 as well) used #5-40 screws in the head, not M3 x 0.6.   There were posts there re this subject saying that they were some sort of weird metric thread.  Not so.

If the OS was to use a #5-40, a tap would have to be run into the M3 hole to allow fitting as there is a 0.007" difference in diameter.

HH

[RandySmith]

If the OS was to use a #5-40, a tap would have to be run into the M3 hole to allow fitting as there is a 0.007" difference in diameter.



Some people do use the 4-40 bolts as they are closer to the original thread used as any US thread.
I have had many 30 and 35S engines sent to me with 4-40 bolts in them
 but best to use the original threads bolts if possible
Randy

[Randy Ryan]

Well, if I go to an inch thread, it'll be a 5-40 because I can run a tap into it and have more thread engagement then with a 4-40. 4-40 major is .112, M3 is .118, 5-40 is .125. Still hoping for the right ones, but its not looking good. I still balk at $4/10 x 7 is $28 and Micro won't give me a bulk discount.

I am always cautious with threads, I'm a designer and have spent allot of time designing bolted joints. Thread engagement in aluminum is pretty important and the basic rule of thumb is 2D engagement and that with proper threads. Tapped to 5-40, I can't get that much engagement because of the pitch difference. Because the metric
.6 pitch thread is finer then the 40 pitch, each thread will get thinner as the depth increases, that's not good.