VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Seat adjusting screw and nut

Does anyone know a source for a nut that will work on a 1931 sedan front seat adjusting screw or the actual specifications for the thread or nut? The nut part of my mechanism is made of pot metal and is broken. I am trying to find a nut that will fit the adjusting screw thread that I can weld into the rest of the seat adjustment mechanism. It appears the thread is 1/2 x 12 tpi., (instead of the common UNC 1/2 x 13) I got a nut with these specifications, but it will not fit. Any help would be appreciated.

What is the condition of the threads on the bolt? If the threads are a little wonky, even a correct nut will not go on nicely.

My old truck Lurch has 1/2" x 6' bars that hold the cattle cage together and they have 1/2-12 threads on the ends. I needed to clean up the threads, but I didn't have a 1/2-12 die. I do have an old die set that has two-piece die halves that fit into a holder and are adjustable in-and-out to get more or less cut on the male threads on a rod or a bolt.

Soooooooo, I used the 9/16-12 die halves and screwed in the adjustment set screw until the opening between the die pieces was 1/2". At this setting, the old threads on the cattle cage rods cleaned up nicely and afterwards, the nuts that I had went on smoothly.

Just makin' do with what I've got laying around.

Cheers, Dean

My threads on the bolt are in good condition, but I will try cleaning them up more. I was thinking of something similar to what you did, using 2 halves of a nut to clean up the threads or to make a usable nut by lining them up and welding the halves back together. Sure would be easier to find a nut.

I don't have one handy to check but was thinking that the threaded rod had Acme threads. They are flat not tapered like the threads we are used to seeing. Screw jacks also used Acme threads. I am sure I will be corrected if my memory is cloudy?

Not sure if the 29 pictured below is the same but I think it is the same as my 31. I need one too. It may be my eyes but the threads on this look more like wood screw threads than normal bolt threads. Is that acme? We could make a new nut if we can get a tap.

Dave

DHarrison, I have a couple of 1/2-12 taps. You can borrow them to experiment with making the nut that you need.

Where in California are you? I live in the SF Bay Area.

Cheers, Dean

Guess my memory was faulty. Those are tapered or angled threads in the photo. If I remember the British 1/2" bolts had 12 not the 13 tpi in the USA.

Dave (Dave39MD), Yes, that is what my 1931 seat adjustment screw looks like. It does looks like it has a lot of "angle" to the threads. Compared to a 1/2 - 12 nut.

Dean (Rustoholic), I live in Placerville, a couple of hours away. If I can't come up with a solution I may take you up on your offer.

For those interested, a little more information as I educate myself on threads. The seat adjustment screw is not an ACME thread. The thread profile is closer to a standard UNC thread with either 55 or 60 degree on each ridge. I have figured out it is a double start or double lead thread, this is why it looks so "angled". There are two threads starting at the same time on the end of the shaft. Consequently the helix angle of the threads is larger and it will move further for the same rotation than a typical standard single start thread. I still have to verify a few pieces of information but it tentatively looks like I need a 1/2 x 12 double lead tap or nut to match the thread.

Great detective work!! I knew the threads were not just normal but didn't know exactly what they were.