MS310X and MS345X interchangeable?

Can anyone confirm that MS310x may be replaced by MS345x connectors? for example, MS3106 → MS3456?

Hello nick4,

Welcome to the DigiKey TechForum.
We do not carry either of the MS3106 or MS3456 connectors, so we are unable to verify if one would be a cross to the other.
You should contact a vendor, that carries these connectors, to get help with this.

But DigiKey does carry them… thousands of them!

There’s some ambiguity of intent regarding the “may be replaced by…” concept.

The wikipedia page and other sources on MIL-DTL-5015 connectors show that the distinction between the series I and III flavors in question involves the nature of the contacts and their assembly; solder vs crimp and front vs rear release.

While completed assemblies of comparable parts from the two series may inter-mate, the practicalities of assembly differ substantially. The degree to which a person is concerned with the latter would affect the answer to the “may be replaced by” question.