Pic 1 - Original US 3/16 pipe and the taps shank & barb

Pic 2 - Original US 3/16" pipe and a UK 3/8" pipe (From Barney)

Pic 3 - Original US 3/16" pipe and UK 3/16" pipe (From Barney)

Pic 4 - UK 3/16" pipe actually slides into the barb and even if I heated it, there is no ways I am going to get it over the top of the barb

Clearly there is a difference in our 3/16" pipe and US (possible they are measuring the internal diameter and we are measuring the external. So my question is
a.) Do I try change the barb and Shank -- OR --
b.) Do I change the size of the tube, it looks like its 1/4"
Any suggestions would be really useful