I am a little confused...
The o-ring is 14.5mm, that does not mean the top connector is sized to 14mm. It could be the ring is sized to compress. I am sure the 14mm o-ring is measured uncompressed. The injectors should have a seat that the ring seats into on the injector when inserting into the fuel rail.
Just my thoughts.. its kinda strange that the seller specifically mentions the 7m though.