I am looking for the general term for any technique used to make sure that two parts can be mated only if they are meant to be mated, and prevent any other parts from mating.

I need this term as I describe characteristics of electrical connectors. But I am looking for the mechanical term for these techniques, not an electrical term.

This is what I have:

  • Polarization: forces you to mate the correct mates in the correct orientation; keeps you from mating them in the wrong orientation; e.g., plugging a polarized plug into an AC power outlet turned 180 degrees

  • xxx: matches the shape and dimensions of two parts (not assemblies) so they fit together perfectly and other parts won't fit. e.g., the differences between an EU AC power plug and a US AC power plug

  • Keying: slight modifications in otherwise identical plugs so that they can only be plugged into the correct receptacles; e.g., removing a pin from a PCB header and blocking the corresponding hole in the plug

I am looking for the proper term for "xxx".

Thank you.

EDIT: best suggestions so far include "conforming", "pairing", "congruence", "fitting".

EDIT: Not "poke-yoke": that's design for mistake-proofing the manufacturing process.

  • $\begingroup$ can it be "mateable"? :) $\endgroup$ Feb 4, 2023 at 19:42
  • $\begingroup$ unique ........ $\endgroup$
    – jsotola
    Feb 5, 2023 at 0:49
  • 3
    $\begingroup$ Have a look at the Japanese poka-yoke. This term is well understood in western manufacturing practices. $\endgroup$
    – Transistor
    Feb 5, 2023 at 8:16
  • $\begingroup$ I am well aware of poka-yoke and many have suggested it. Thank you, but that's not the word. poka-yoke refers to making an assembly fool-proof. I am not asking to make an assembly fool proof. I am asking about making two parts match and fit each other perfectly. $\endgroup$ Feb 5, 2023 at 12:29
  • 1
    $\begingroup$ How about Paired? $\endgroup$ Feb 5, 2023 at 14:59

1 Answer 1



Thank you all.

It's now in the book.

2.6.6 Polarization, conforming, and keying

Polarization, conforming, and keying are three technologies that ensure that two mating parts fit perfectly. Where they differ is in what they prevent from mating:

  • Polarization: prevents mating the correct parts in the incorrect orientation (fig. 2.109a)
  • Conforming: prevents mating the incorrect parts (fig. 2.109b)
  • Keying: prevents mating to a nearly-identical part that must be mated elsewhere (fig. 2.109c)

Book screen shot


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