7/8x14NC vs 7/8x14NF Threads...

[BCB]

I know that the threads on presses and dies are the 7/8x14NC yet they make a 7/8x14NF die…

What is the difference between the NC and NF thread? Both 14 threads per inch—right?...

Thanks…BCB

[Jim]

I know that the threads on presses and dies are the 7/8x14NC yet they make a 7/8x14NF die…

What is the difference between the NC and NF thread? Both 14 threads per inch—right?...

Thanks…BCB

7/8X14 is National Fine, 7/8X9 is National Course.

[BCB]

7/8X14 is National Fine, 7/8X9 is National Course.

I just purchased a 7/8"x14 NF and it runs on dies quie difficult. So difficult that I didn't screw in to on clean the threads...

Yet, I have a 7/8"x14 NF tap and it screws into the RCBS press easily...

I wonder what the difference is.

Why 2 designations for the same thread--NF or NC?

Or, are they not the same thread-pitch difference etc...

Thanks...BCB

[Jim]

I just purchased a 7/8"x14 NF and it runs on dies quie difficult. So difficult that I didn't screw in to on clean the threads...

Yet, I have a 7/8"x14 NF tap and it screws into the RCBS press easily...

I wonder what the difference is.

Why 2 designations for the same thread--NF or NC?

Or, are they not the same thread-pitch difference etc...

Thanks...BCB

They are NOT the same thread count. National fine threads have more threads per inch than National coarse. That's why they have different designations.

Study THIS CHART (http://www.unionmillwright.com/2879.pdf).

[BCB]

Or, as I think about this, is a 7/8x14 always going to be an NF?...

And for a 7/8” bolt to be an NC it would have to be 9 tpi?...

[BCB]

Or, as I think about this, is a 7/8x14 always going to be an NF?...

And for a 7/8” bolt to be an NC it would have to be 9 tpi?...

I think I just answered my own question now...

[Reg]

7/8"x14 (tpi) is National Fine
7/8"x9 (tpi) is National Course

Nair the twain shall meet.

For further information, study the Machinery's Handbook.

[BCB]

7/8"x14 (tpi) is National Fine
7/8"x9 (tpi) is National Course

Nair the twain shall meet.

For further information, study the Machinery's Handbook.

Yep, I believe I answered my own question in the previous post...

Sometimes a person needs time to think--and for me that can take days...

Thanks Jim and Reg...

[W.R.Buchanan]

If the threading die you mentioned has a screw adjustment on it then the pitch diameter of the male thread on the reloading die is probably correct and the threading die just needs to be opened up until it's pitch diameter is the same or bigger to go on the male loading die. IE it will screw onto the Reloading die but not cut metal. It could be used this way to chase gooned threads.

Most quality dies have this adjustment and this is done to facilitate cutting tighter or looser threads as needed.

Taps are not adjustable but come in many + or - sizes depending on what is needed.

If you are making a part that is going to be plated after it is made then an oversized tap is used to cut a bigger thread that will be closed back down to nominal size by the plating material.

Same is true with cutting an OD thread with a die. If the part is to be plated then a smaller "Pitch Diameter" is required so that when the plating adds material the pitch diameter is increased into the nominal range for that thread.

Hope this helps with understanding of this subject.

Randy

[BCB]

If the threading die you mentioned has a screw adjustment on it then the pitch diameter of the male thread on the reloading die is probably correct and the threading die just needs to be opened up until it's pitch diameter is the same or bigger to go on the male loading die. IE it will screw onto the Reloading die but not cut metal. It could be used this way to chase gooned threads.

Most quality dies have this adjustment and this is done to facilitate cutting tighter or looser threads as needed.

Taps are not adjustable but come in many + or - sizes depending on what is needed.

If you are making a part that is going to be plated after it is made then an oversized tap is used to cut a bigger thread that will be closed back down to nominal size by the plating material.

Same is true with cutting an OD thread with a die. If the part is to be plated then a smaller "Pitch Diameter" is required so that when the plating adds material the pitch diameter is increased into the nominal range for that thread.

Hope this helps with understanding of this subject.

Randy

The threading die does not have an adjustment screw—I did see those and they were 4 times the price of a threading die that I purchased—I purchased the inexpensive one just to clean the threads on the reloading dies…

I was trying it on a truck tire stud that has the 7/8”x14 thread and it was working extremely difficult—don’t know why, but maybe sloppy tolerances on the stud as it might not need to be real precise…

I finally tried it on a reloading die and it actually worked quite smoothly. I was quick to judge without really checking things out…

I understand what you are saying about plating etc…

I think I now have an inexpensive threading die and a fairly expensive tap (a gift from a machinist who earns his living with such tools) and I can now “clean” the threads, on the press and dies, once in awhile as crud builds up on them…

The ones I cleaned screw into the press with ease…

Project completed—I think…

Thanks…BCB

[I'll Make Mine]

I was trying it on a truck tire stud that has the 7/8”x14 thread and it was working extremely difficult—don’t know why, but maybe sloppy tolerances on the stud as it might not need to be real precise…

Dirt, corrosion, thread damage at the end of the stud (from impacts and partial cross threading), all very likely conditions for a lug stud.

[MtGun44]

Tolerances is what you are seeing. 7/8-14 is 7/8-14 and there is no UNF version and
UNC versions with the same number of threads per inch. The UNC 7/8" thread has
9 threads per inch and the UNF version has 14 threads per inch. Both have 60 deg
thread form.

Your dies are maybe a few thousandths oversized and the press thread a few
thousands large, too.

Bill

[geargnasher]

Dirt, corrosion, thread damage at the end of the stud (from impacts and partial cross threading), all very likely conditions for a lug stud.

Let's not forget pitch change from overtorquing and hammering the stretched nut back off the stud.

Gear

[quasi]

a good quality die is adjustable, taps come in different grades (sizes) to achieve different classes of fit. See Machinerys Handbook.

[BCB]

Yep, I thought there might be some tolerance differences as mentioned...

Now that I have worked with them a bit, I think they will do what I want them to do...

I have tried the thread die on several reloading dies and they all work smoothly. I guess I just panicked when the threading die wasn't doing such a good job on the truck wheel lug...

As far as the tap and die performing on my reloading stuff--all seems good. Nice clean threads noted and the reloading dies screw into the press with no exertion or binding at all...

Thanks...BCB

[W.R.Buchanan]

The pitch diameter is a range. Generally there is .002-.005 thousandths depending on the size of the thread, IE; the larger the thread, the larger the window. The difference bewteen a Class 2A and 3A thread is just a narrower window. The 3A is tighter than a 2A. 2A is most common and usable for virtually everything there is. However occasionally a 3A fit is required if the thread must perform a duty other than just holding something together.

I would expect a barrel thread for a compensator to be a 3A class of fit, simply due to the need for the thread to locate the compensator both axially and radially so the bullet doesn't bounce of the bore of the compensator. I would also expect to see a register on both ends of the thread to also locate the compensator.

Generally a fixed die will be ground to produce an OD thread which is on the lower end of the pitch diameter. The thread that is generated is still within the tolerance window, but since it is on the low side the part will fit more ID threads than one that was made to the high end of the pitch diameter window. Seems logical right?

Hexagon Thread Repairing Dies are generally ground on the high end of the PD window. This is because they don't want it to cut material, they just want it to remove the gooned areas of the thread. IE they don't want to change the PD of the existing thread.

I would not hesitate to chase a hole in a reloading press with the 7/8-14 tap I have. First the tap is a standard size tap, so if it cuts metal going thru the press, the hole probably needed to be chased anyway. My C&H H frame press got this treatment, and works much better as a result.

Chasing a loading die is another matter, if you start the die onto the thread and it starts cutting material you might be better off just backing it right back off and cleaning the threads up with a triangle file, and a trip to the wire wheel.

Some common sense is usually a good thing when messing with stuff.

Randy

[BCB]

Yep, I didn’t force any of the thread work I was attempting…

It did require some effort to clean the threads on the wheel lug, but it didn’t matter if that got ruined or not. But, after I had cleaned about an inch of the threads, I tried to screw it into the press and it was as smooth as cutting butter. So, it did work fine…

The tap went into the press with no problems. I could fell it become a bit loose and a bit tight as I turned it. Never any great torque used to turn it though. The threads were clean and like new…

The threading die screwed onto the reloading dies with no effort at all. Probably just removing some dirt that had accumulated on the occasionally used oil I put on the threads…

So, all in all, both tap and threading die work well for what I purchased them for…

Many, many years ago, I purchased a Craftsman tap and die set. It has about 35 taps and the same number of dies, or close to the same number. I have used it numerous times and it does a good job and has saved a few nuts and bolts that needed used again and again…

I don’t even see that same set offered anymore. Just smaller sets and they are very pricy. I know mine didn’t cost what the lesser quantity sets cost today…

Always learn something on this site for sure…

Thanks…BCB