On Monday, 26 December 2016 14:45:24 UTC, Dave Plowman (News) wrote:
TLC sell 'bridge' units that connect any two standard metal boxes together
at the right spacing for the plates.

FSVO plates, possibly.

Personally I dislike abutted flush faceplates.

A couple of conduit bushes and a coupler will tie boxes together nicely.

Owain