Odd thread size

[Florida Rookie]

I have special screws on a commercial machine that need to be replaced which i cannot identify. The machine is made by Toyota. The screws are close to 8-32 and 4-70mm but neither are the right pitch. I believe i remember something about different metric sizes but i thought that was only special British sizes or something to that effect. Any ideas?

[JCHannum]

While there are thread standards, there is no regulating body that jails those who chose to use their own threads for specialized applications. There are a whole list of special threads, and almost any screw size can be had in any thread count desired. 8-32 is coarse, 8-36 is fine, but 8-40 is a very common thread used on firearms.

If it is a non-critical application, and 8-32 is close, is it possible to chase it out with an 8-32 tap, or go to the next size and use a 10-32 tap and fasteners?

Welcome to the board.

[Andrew_D]

The screws are close to 8-32 and 4-70mm but neither are the right pitch.

4-70mm???? 4mm diameter and 70mm between threads...Wow, that is one course thread...

I assume you meant to say 4x0.7mm???
32 threads per inch would actually be closer to 0.8mm than 0.7mm (25.4/32 = 0.79375).
As mentioned above though...if it isn't "standard" (whatever standard is), then it could be anything. That's what thread gauges are for.

Andrew

[bob ward]

Standard metric threads in your size range, ie screws that you should be able to buy, are 4mm x .7mm, 4.5 x .75 and 5 x .8

There is a series of metric fine threads but the smallest is 8 x 1.0

If your problem screws are specials you will have to talk to Toyota or make them yourself.

Welcome to the board and let us know how you get on

[Florida Rookie]

4-70mm???? 4mm diameter and 70mm between threads...Wow, that is one course thread... Andrew

OOPS! In my defense however, the hardware store did in fact list them at 4-70 in the bin and i guess it was in my brain. Forgot to print the dot i suppose.

Thanks for the help guys and the welcome aboard. The screws are special with oddly flanged ends and while i do have a home project type mill/lathe combo, time is severly lacking at this point. I could make a new nut (which is also special but easy to make) which is what needs repaired and what i am trying to do but i just can't find the right size to use. I would heli-coil but doubt if i could find one when i do identify the thread size. On the metric side, .75 is too narrow and .80 is too wide. On the sae side, 36 is too narrow and 32 is too wide. That's using a good quality pitch guage. (Matco) I am substituting with a screw and nut for now but that is a complete pain in the tail.

[Carld]

I would email the factory and tell them exactly what you have and ask them what the thread size is and if they can supply the screws you need. They may actually help you out.

[Florida Rookie]

I can order the parts but need them now. I guess i can get by with screw and nut for now and order them monday. I think i'll take your advise though Carld and get the size so i can make a few extras. The nut is 1/4 inch brass rod that is drilled and tapped and they strip often. The special screws hold up well so i just need a few spare nuts. To get the nuts though, i have to buy an assembly which is not cheap.

[RobbieKnobbie]

If the nut is brass, can you take one of the screws (which I assume are steel), grind a little cutting edge or two into it and call it a tap?

[Florida Rookie]

If the nut is brass, can you take one of the screws (which I assume are steel), grind a little cutting edge or two into it and call it a tap?

That's an idea. I'll give it a try. Thanks.

[SDL]

Standard metric threads in your size range, ie screws that you should be able to buy, are 4mm x .7mm, 4.5 x .75 and 5 x .8

There is a series of metric fine threads but the smallest is 8 x 1.0

If your problem screws are specials you will have to talk to Toyota or make them yourself.

Welcome to the board and let us know how you get on

I believe fine goes down to M1, see here

http://www.engineeringtoolbox.com/metric-threads-d_777.html

Steve Larner

[bob ward]

I believe fine goes down to M1, see here

http://www.engineeringtoolbox.com/metric-threads-d_777.html

Steve Larner

Thanks for that Steve, I've learned something today.

[Florida Rookie]

If the nut is brass, can you take one of the screws (which I assume are steel), grind a little cutting edge or two into it and call it a tap?

I did pick up some 1/4 brass rod and make a tap out of one of the screws. It worked! Thanks for the idea Robbie. I'll punch out a few spares later but this got me going for the weekend. Of course, i hate working on the weekend but business is business these days. Thanks for getting me going. I never thought of that.

[john hobdeclipe]

I just pulled down an old catalog from Metric Fasteners Of Charlotte (NC) and they list a M4X.75, M4X.7, and M4X.5

The last time I was in there (about 13 years ago, when I lived in the area) one of the owners showed me a cabinet full of hundreds of odd size/pitch taps & dies. If you can accurately determine the pitch, it may be worth a call to them to see if they have it in their oddball cabinet.

Since you've now successfully created a part with matching female threads, you can use a micrometer to measure how far the screw moves over multiple turns, then divide by the number of turns and get an accurate pitch reading.