Confused and need information about Threads

[DAVIDMAGNUM]

Greetings and thank you for reading this.

I recently discovered that the beginning threads on my Rock Chucker press are buggered up. The threads inside of the thread adapter/bushing. I looked online and the RCBS 09138 Bushing is not widely available . I have a few taps for my job so it was worth a try to clean the threads. What I found has me confused and searching the internet for an answer was useless. Standard reloading dies are 7/8-14 threads, right ? Then why is my 3/4-14 tap too large to even start to enter the adapter? Is there a size/measuring difference for NPT and "machine" threads?
If you know please let me in on the little secret.

David

[elmacgyver0]

I believe the "3/4" is the inside diameter of the pipe, so the size would actually be larger to account for the material thickness of the pipe.

[M-Tecs]

Pipe threads are taped and sized off the ID of the pipe. NPT is the abbreviation of National (American) Pipe Thread. It belongs to the American standard 60-degree tapered pipe thread and is used in North America.

Call RCBS they will send you a new one. They may send it for free. For thread damage I cannot say but RCBS did make a batch that the inside thread was not parallel to the outside. They did replace those for free. Couple of years back a friend was having runout issues. I tracked it down to a bad bushing. Call RCBS and he had it in a couple of days.

[45_Colt]

Greetings and thank you for reading this.

I recently discovered that the Standard reloading dies are 7/8-14 threads, right ?

Yes, standard straight SAE (machine) thread.


Then why is my 3/4-14 tap too large to even start to enter the adapter? Is there a size/measuring difference for NPT and "machine" threads?

David

As others posted/mentioned, NPT is a whole 'nother story. Wouldn't want to use it even it it did fit, as they are also tapered.

45_Colt

[Der Gebirgsjager]

Yup- go the simple route and replace the bushing.

DG

[GWS]

There IS another option........;)

I wanted to use the Lee Breech Lock Die system on my Rock Chucker.......easy peasy.......

https://www.leeprecision.com/1-1-4-12-bl-update-kit

Yes that's a bushing that screws right in to your Rockchucker.....love the change.

[hoodat]

But Wait!! There's more!!! Options that is.

Old Okie method of thread repair without buying a big expensive tap is this. Get a bolt of the correct size and thread pitch, (the harder the better), or even an old die body that you don't need. Take your angle grinder with a cut-off disc, and cut grooves across the threads, for at least the bottom few threads. This is now your improvised thread chaser and will work to carefully clean up the damaged thread or threads that need it. jd

[jmorris]

Standard reloading dies are 7/8-14 threads, right ? Then why is my 3/4-14 tap too large to even start to enter the adapter? Is there a size/measuring difference for NPT and "machine" threads?

Pipe is ID. The drill size to tap a 3/4 NPT hole is 59/64 (larger than a 7/8 hole, even if it doesn’t have 14 threads per inch in it).

[DAVIDMAGNUM]

Pipe is ID. The drill size to tap a 3/4 NPT hole is 59/64 (larger than a 7/8 hole, even if it doesn’t have 14 threads per inch in it).

Thanks
That is what I was looking for. I guess that I just didn't ask Google the right questions when I was doing the search online. RCBS has the part in stock.I was surprised to ge an email response first thing Monday morning. I only use the single stage press to size bottle neck cases and deprime wet cases. So I don't need to convert to a quick change.

[Soundguy]

thread repair file will be your fastest.. new lee or rcbs busing also good ideas.. depends if you have a thread repair file in a local store near you. they are usually about 8" long.. and square/rectangular in profile.. and have a different thread pitch file on each of the 4 sides.. top and bottom.. so 8 threads. pick one close and get at it.. once you can get a die going in.. straight.. you are golden.. first few threads being short won't matter much.

https://www.acehardware.com/departments/tools/hand-tools/files/27955?store=06851&gad_source=1&gclid=CjwKCAjws9ipBhB1EiwAccEi1DdgSFVZwDJbwnC4G_ow mtqsNS398Q1haGMTJ6-BlNm5ZViTDuvZGhoCyFUQAvD_BwE&gclsrc=aw.ds

[GWS]

Thanks
That is what I was looking for. I guess that I just didn't ask Google the right questions when I was doing the search online. RCBS has the part in stock.I was surprised to ge an email response first thing Monday morning. I only use the single stage press to size bottle neck cases and deprime wet cases. So I don't need to convert to a quick change.

I was looking for you, for the bushing part # on RCBS's site.....and that was a tall order, (both RCBS and Lee have made their websites harder to find anything, in the name of progress?).....I was next going to say call RCBS.....but you already figured that out.

I use both the Lee Breech Lock version of the bushing and the RCBS screw-in version, which is standard 7/8"-14 thread inside, and 1-1/4"-12 outside ..... both bushings screw into the RCBS RockChucker, Summit, or Rebel presses......makes them very versatile indeed. Thought you might find the Lee version a good option to have around......I was surprised to find the Lee part is aluminum.....which is fine for its intended use.

[jmorris]

https://www.midwayusa.com/product/1012164380?pid=824687

Says discontinued but does give you the mfg part #.

[elmacgyver0]

Pipe is ID. The drill size to tap a 3/4 NPT hole is 59/64 (larger than a 7/8 hole, even if it doesn’t have 14 threads per inch in it).

I guess nobody believed me when I said it.

[M-Tecs]

thread repair file will be your fastest.. new lee or rcbs busing also good ideas.. depends if you have a thread repair file in a local store near you. they are usually about 8" long.. and square/rectangular in profile.. and have a different thread pitch file on each of the 4 sides.. top and bottom.. so 8 threads. pick one close and get at it.. once you can get a die going in.. straight.. you are golden.. first few threads being short won't matter much.

https://www.acehardware.com/departments/tools/hand-tools/files/27955?store=06851&gad_source=1&gclid=CjwKCAjws9ipBhB1EiwAccEi1DdgSFVZwDJbwnC4G_ow mtqsNS398Q1haGMTJ6-BlNm5ZViTDuvZGhoCyFUQAvD_BwE&gclsrc=aw.ds

How do they work on internal threads per the OP's needs?

[GWS]

https://www.midwayusa.com/product/1012164380?pid=824687

Says discontinued but does give you the mfg part #.

Now we're going to really confuse him! :) Look closer....that's not the same part made for the Rock Chucker....that's a part to convert older presses that used larger die threads to convert to the now most common 7/8" 14 thread. Outside thread is also 14 per inch. See below:
319185

The RockChucker part is 12 threads per inch.....I took a crappy picture of my RockC. part....think you can still see the difference.....no wonder the one on Midway is discontinued......they probably can't sell the part pictured above too often anymore.

319184

The one RCBS will send him will be right as long as he said it goes on the RockChucker.

The old RCII part is 09138
RCIV part # is 709138
Summit and Rebel part # is 7709138 all the same part.

[country gent]

You can use a smaller tap with the same pitch in this case 14 threads per inch by scraping thru the thread with one flute. work the damaged area. Inking in the threads will show progress The machinists handbook is a great source for information on threads and fits.

[nicholst55]

I bought a chinesium tap and die on Amazon to chase the threads on an old Lyman turret press with for $25. It worked perfectly for the job. In fact, I spun the tap with my fingers. The very top of three die holes were dinged, and this cleaned them right up.

https://www.amazon.com/gp/product/B071GN4RVJ/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

[M-Tecs]

Parts list here.

https://www.rcbs.com/on/demandware.static/-/Library-Sites-HuntShootAccessoriesSharedLibrary/default/dw97840776/productPdfFiles/rcbsPdf/Parts_Book.pdf

[G W Wade]

RCBS sent me a new bushing earlier this year. For free and a new empty primer tray. GW

[GONRA]

GONRA nos this is NOT wot ya wanna hear -
but it's GOOD IDEA to get a TAP & DIE for threads you notice
on yer reloading equipment to chase / cleanup
dirty / buggered threads .

Start off with 7/8 - 14.
Do NOT get "NPT" or other PIPE THREADS! !!
"Cheap" imports / used / etc. will do Just Fine.....
(INCH tread pitch GAGES are really handy too! )

BUT FIRST - get educated on pipe and machine threads....