I would like to know the name/type of this connector:

DC power plug

It provides 12 DC power to a hand drill, its diameter is about 2.5mm. I would like to buy an adapter for it that converts it to a 4mm banana plug (so I can use the drill from a laboratory power supply).

  • \$\begingroup\$ this totally look like a <insert correct number here>mm banana plug. \$\endgroup\$ Sep 13, 2014 at 9:57
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    \$\begingroup\$ Why not just cut the plugs off, strip the wire ends and fit 4mm bananas. Cheaper option. \$\endgroup\$ Sep 13, 2014 at 10:31
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    \$\begingroup\$ Banana plugs have springs that look vaguely like the skin of a banana. I think these are pin plugs, From memory some of my father's 1940's test equipment used them \$\endgroup\$
    – pault
    Sep 13, 2014 at 10:58

2 Answers 2


Even tough it may resemble one, this is NOT a banana plug:

  • It is a 2.5mm pin plug or 2.5mm male pin connector.
  • It is appropriate for low DC (<=60V) or AC (<=30Vrms) voltages and up to a relatively high amount of current, possibly up to 10-15A, depending on the mating subtype and quality of manufacturing.
  • It usually comes in two variants:
    • Those where the plug is solid, with no slots, designed to be mated to a pin socket or pin jack with an internal longitudinal spring. Note the spring in the socket is key to ensure the electrical connection.
    • Those where the plug is slotted (like the one in your photo). These are usually mated to a pin socket or pin jack with a precisely machined internal bore, requiring no internal spring in the socket. Here the electrical connection is helped by the two halves of the pin plug, pointing slightly outward, acting as an unreliable spring. If the connection fails, one would usually use a flat type screwdriver "separate" a little bit more the two halves of the pin.
  • Note that the two subtypes above are not usually interchangeable: i.e., you will not get a reliable connection between a solid pin plug and a pin socket with no internal spring.

This kind of connector was designed and common use 100+ years ago! It is nowadays a not very common type of connector. Not much cheaper than other similarly cheap connectors and, in fact, much less reliable than those other equally cheap connectors.

I suggest you don't invest too much time looking for a "pin socket to banana plug adapter".

You can easily replace your current pin plugs with a pair of solderable banana plugs. Check also that your laboratory PSU can deliver the amount of current required by the drill.

How to solder a banana plug: https://www.youtube.com/watch?v=Tc0qvbbLL5Q

P.S.: This kind of connectors were mostly employed along with control panels, wiring panels, "plug boards" or training kits, where one had/could manually "rewire, finish or complete the electrical circuit".

As an example, you can find below a "plug board" for an IBM 402 accounting machine.

"Plug board" of an IBM 402 accounting machine.

Photo taken by Chris Shrigley in May, 2003. Explicit permission granted to upload under Creative Commons licence by Attribution. agr 18:01, 19 January 2006 (UTC).


Google "Banana Plug Adapter" for zillions of hits like this one.

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    \$\begingroup\$ This is not a Banana Plug. It doesn't have a "spring mechanism in the plug". It also has not the right dimensions. \$\endgroup\$ Sep 13, 2014 at 13:28
  • \$\begingroup\$ You're wrong, it is a banana plug, and it has a leaf spring arrangement - which is the contact - on the plug end, and is designed to plug into a 4mm diameter hole in the jack. Its female end is designed to accept a smooth 0.080" diameter "pin plug", which your plug should have no trouble fitting into. \$\endgroup\$
    – EM Fields
    Sep 13, 2014 at 14:02
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    \$\begingroup\$ Banana plugs are 4mm, not 2.5mm. Banana plugs must have a longitudinal spring. In fact, banana plugs may be seen as an evolution and improvement over much older pin plugs. Banana plugs are not slotted... \$\endgroup\$ Sep 13, 2014 at 17:33
  • \$\begingroup\$ I googled around a bit more and I tend to agree with others here, that it's a pin plug. I found several 2mm (mini banana plug) to 4mm (normal banana plug) adapters, so 2mm seems to be some standard size for mini banana plugs, but couldn't find anything for 2.5mm. That said I also saw 4 leafed banana plugs like link, so mine could be a 2 leafed banana plug as @EMFields said. I decided to simply replace them with normal banana plugs as suggested. \$\endgroup\$
    – Imre Deák
    Sep 13, 2014 at 17:42

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