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I am attempting to get two probes through a sealed case to detect the pH of a fluid like water.

My thought was to get two header pins and seal them with a custom 2mm diameter seal. However it looks like most header pins are square. Are there round ones? Or something similar not called a header pin? I trust sealing on a round surface better than a square surface.

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    \$\begingroup\$ They are called machine pins or machine socket pins. \$\endgroup\$ – DKNguyen Jul 21 '19 at 21:53
  • \$\begingroup\$ Have a look for 2mm sockets (a smaller version of the 4mm banana plugs). These take 2mm multimeter probes, etc. The panel mount version of these should be waterproof. \$\endgroup\$ – Transistor Jul 21 '19 at 21:54
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    \$\begingroup\$ They exist, but do not sound like a good idea for your usage. Fluid sealed contacts and connectors actually turn out to be a very challenging problem. \$\endgroup\$ – Chris Stratton Jul 21 '19 at 22:27
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    \$\begingroup\$ @DKNguyen machined pins. \$\endgroup\$ – Marko Buršič Jul 21 '19 at 22:33
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There are definitely round shaped header pins - just try a web search for ‘round header pins’ and you will see many. However, as Chris Stratton points out, fluid tight seals are somewhat tricky - for example, you can’t just surround the pin with another solid material and achieve fluid isolation. Typically a connection would need either a glued (like epoxy) seal between the two materials or else (depending on the fluid pressure) some sort of compression seal (multi conductor circular connectors in military applications typically go this route).

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