Im completely rewriting my question to better clarify my question.

I came into possession of a oscilloscope and tone generator (see below) from the early 1960s. They didnt work and upon looking at the 1960s electronics inside, I had no desire to repair them. However, they would be great for an Arduino or Raspberry Pi. I am going to restore the outside of the units. I decided to gut the insides of both units, completely stripping the electronics out. After researching the units, I found out both of these were kits that someone put together and soldered by hand. I applaud whoever did this, they had far more patience than I would have had. The original owner is probably turning in his grave after what I did to his equipment. Actually, there is chance he might still be alive. But I digress...

As I said before, I am not trying to repair these units. They have been stripped bare. I removed the knobs from their posts. I was able to clean and restore the knobs. Since the knobs have a distinct look, I wanted to use them if possible. I want to put some modern switches/potentiometers in their place and attach the old knobs to them. The posts look like the picture below.

So I was asking what is the name of the parts I should be looking for?

Dampmaskin answerd the question in the comments saying D-Shafts. Many of the original dials are doubled up, with one dial pointing above and the other pointing below. If I can find a D-shaft that can accommodate both, that would be awesome. However, I would settle on removing the bottom dials if I need to.

enter image description here enter image description here

  • 1
    \$\begingroup\$ Really hard to say from an image. It looks like a co-axial potentiometer, but is could also be a variable capacitor or other non resistive element. \$\endgroup\$
    – Trevor_G
    Apr 15, 2017 at 21:37
  • \$\begingroup\$ @Trevor I am not to fix this machine. I will remove these potentiometers and replace them with new ones to hook up to an Arduino. I just need to know what type of switches/potentiometers have this type of post. \$\endgroup\$
    – Keltari
    Apr 15, 2017 at 22:32
  • \$\begingroup\$ Why do you want to replace them, are they oxidized, seized up or otherwise damaged? Otherwise you could just desolder them from the existing connections and connect your arduino to them. \$\endgroup\$
    – jms
    Apr 15, 2017 at 22:48
  • \$\begingroup\$ @jms they are quite crusty, rusty, and nasty. \$\endgroup\$
    – Keltari
    Apr 15, 2017 at 22:51
  • \$\begingroup\$ If you mean the shafts, and you want to reuse your old knobs with new pots or encoders, I believe they're called D-shafts because of the shape. Might come in different sizes, so measure them before you order anything. They also look unusually long compared to newer pots I've seen. \$\endgroup\$
    – Dampmaskin
    Apr 15, 2017 at 23:15

2 Answers 2


One of the largest component suppliers in the UK /World calls them flat shafts. However, these are uncommon today and I can only find a very few on the RS Components web site. They mostly seem to be fully round. They typically come in 6.00 and 6.35 mm diameters so aim for the same size, but I guess 0.35 mm is neither here nor there for a knob control. 6.35 is closest to 1/4 inch for your old dials.

Don't let that bother you. Get some of these:-

needle files

They're designed for putting flats on pot shafts. I don't care what sort of ultra sophisticated engineer you think you are, if you haven't got any files then in my mind your not a real engineer :-)


Stuff it. Following your edit with the additional photos, Trevor's right below. You'll have a very hard time finding a fine /coarse pot these days. But that's irrelevant. If you're trashing the insides and going digital, then the control panel doesn't have to have full original functionality. You'd find it difficult to replicate that functionality anyway. Just use normal potentiometers instead. You could of course rename the dials and have a dedicated fine and dedicated coarse knob instead sacrificing some others.


Really hard to say from an image. It looks like a co-axial/concentric potentiometer like the one below, but its could also be a variable capacitor or other non resistive element.

enter image description here

You may be out of luck for a replacement. Things of that vintage were often custom made for a particular product. I stand by the coaxial-part, there was probably two knobs on there at one point.

Anyhow, you would need to post a picture from the other side for anyone here to really be able to guess what is it.

Even if you can be sure it's a potentiometer, co-axial ones are pretty hard to come by. They are usually considerably more expensive than the regular variety too.

  • \$\begingroup\$ I think that I mistook the photo That's a second notch isn't it? That's a fine /coarse adjustment pot. You're correct of course Trevor. \$\endgroup\$
    – Paul Uszak
    Apr 16, 2017 at 13:06

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