I wasn't going to cover cutting threads in a steel rod but a miscalculation on my part caused me to haul out my button dies, so here goes.
When I started assembling my console table I realized that I forgot to buy jam nuts and because I didn't buy jam nuts my calculation on how much threaded area was needed was incorrect. I needed at least another half inch of threads on each end of the thicker rod. So I hauled out my button dies.
Button dies are the round disc that cuts the threads on pipe or rod or you can sometimes use them to correct a damaged area on a bolt. More than likely the average homeowner won't have a variety of button dies or corresponding taps but I used them when I was working so I dusted off the old toolbox and found my stash of button dies. I also realized someone has been in my toolbox because I have a method to storing my tools and I found wrenches in my socket drawer and basically everything was a mess. This screams R all over it.
I keep my button dies and some of my taps in a metal box. I have another plastic container with my tiny taps, and then of course I have my three tap and drill indexes. But what I needed today was a button die and a die handle (some call them a holder or wrench).
Each button die is marked with the type of thread such as NC, NF, NPT, and NPS. NC is national coarse, NF is national fine, NPT national pipe thread taper, and NPS national pipe thread straight. There are others but since I wasn't threading pipe I was only concerned with NC and NF button dies.
A quick look at the threaded rod, bolt or nut should tell you whether it is a fine thread or coarse thread. Now you measure the rod or bolt to get a size. I purchased the rod so I knew it was 3/8th. So I know it's 3/8th and it NC. But I also need to know how many thread per inch. This is important because if the thread count is off then the pitch of the threads will not be correct and match your nut or match the threads if you are adding threads like I was today.
You can use a thread gauge or in my case I had the rod with the threads already cut and just needed to match up a die. Because of my past experience I did grab the correct button die to begin with, which was a 3/8 NC 16. This translates into a 3/8th stock, national course threads, 16 threads per inch.
To double check, try spinning the button die onto the rod or bolt. If it is correct it should easily spin on. If you have to try and try to get it started and it snags along the way it is the incorrect thread count. DO NOT FORCE.
Next you put the button die in the die handle. You will notice a little indent on the die. Line this up with the set screw and tighten the set screw.
Now look for your bottle of thread cutting oil or compound. I gave up after 15 minutes and just used some 3 in 1 oil that was sitting on the workbench. Now if I was doing precision work I would have looked until I found my bottle because I would need the nicest threads possible.
Place your rod in a vise and clamp tightly. You can place your rod either straight up and down or horizontal. It just depends on how you like to work. I'm a straight up and down person because I find it easier to keep my button die handle level in this position.. Next lubricate your rod with cutting oil.
The first couple of threads will be the hardest and the first thread may even be crooked but by the time you finish, it will be OK. It's important to keep the handle level until you have several threads cut. After that the die will keep the handle in the correct position.
Turn your handle a half of turn and then back about a 1/4 turn, then forward a half of turn, and repeat the process, When you go backwards it removes the waste metal (shavings) out of the way. If the metal looks dry or the cutting is difficult, add more oil or compound. You cannot add too much oil.
If you are doing multiple pieces and you want the threaded area to be the same length you will need to count the revolutions. Today I needed to add 9 revolutions to each end to get the desired additional thread length that I needed. 16 threads per inch and I needed 1/2 inch more threads so I chose 9 revolutions. 8 would have been 1/2 inch but I added one revolution for good measure....LOL
Now I could assemble the base. First screw on the jam nut. The jam nut goes on all the way until you run out of threads. Next put the rod through the base and screw on the brass acorn nut until it bottoms out. To tighten, hold acorn nut in place with a wrench or socket and use another wrench to tighten the jam nut against the cast iron. Repeat process on the other end. I have two rods to install and they are different size rods because the existing holes I had to work with were different sizes but the process is the same.
I added these vinyl pads to the top of the base to cushion the glass and to help hold the glass in place.
I shot this photo with my phone and it makes the base look like it is askew but trust me the sides are straight up and down. Tomorrow I will clean the glass, take a better photo, and I'll have a console table to use on my deck.
Reuse, Repurpose, Recycle
This is the mechanical part of the oak desk chair. After dis assembly, I used paper and tape to protect the machined areas during the next step which was sand blasting. Once all the parts were sand blasted and the loose grit removed with an air gun I inspected all the parts. One of the long threaded bolts had damage to the threads. I had several options for restoring the threads. One was to use a thread chaser which is similar to a file but has four sides with different spacing between the teeth. Or I could use a die and run the bolt through the die to clean up the threads. Either method requires that I use a thread pitch gauge to determine the pitch (threads per inch). 
Here's a closer look at the damaged threads and the thread pitch gauge.
Here is the button die that I used to clean up the threads. The long file shaped tool is the thread chaser. When using a button die or tap always use a lubricant. I use tapping compound but you can also use a 3 in 1 oil if you don't have tapping compound. Depending on the severity of damage, you may need to back up (reverse), clean out the debris from the die and start again. After I chased the threads I re sand blasted the bolt to remove any residue so that primer and paint will adhere to the bolt.
Here is everything reassembled and ready for primer and paint. At one time someone must have broken the spring and replaced it. The spring that is currently there is the wrong size spring. It is the correct length but the diameter of the spring is too small and does not seat itself correctly on either end. R will have to shop around and get the correct one.
This weekend we will glue the wood part of the chair where the individual pieces are loose. I'll wait to stain and clear coat when I am using the stain on something else. For those interested...the chair was manufactured by the Colonial Chair Co. in Chicago.