Ecoboost wet cambelt width

[Davep23]

Hi all, I'm going to replace the wet belt and wish to buy the parts prior to starting the job, some are 16mm width and some 18mm. One supplier said a 16mm can be used in either instance but don't use an 18mm in place of a 16mm. Anyone else heard this, are the tensioners the same width. Why was the change made. I'm trying to avoid tearing it apart measuring and then having to wait for the spares. Dave