I use KMC chains and "Missing Link" connectors. KMC recently introduced new models of the "Missing Links" in different sizes. From what I've read, the new models are wider than the original parts. I don't remember for sure which version of the "Missing Link (Original or II) is .2mm wider.

So at least for KMC connector links, you need to know the width of the chain you you are joining, to figure out which "Missing Link" you need to join it.