Thanks George.
The 1/4" valve I am looking at has a stated "orifice" size of 4,8mm.
I assume the stated orifice is the diameter of the ball bore, and being the smallest constriction in the valve, correlates to the DN.
The 3/8" valve has a stated orifice of 7,1mm.
I suppose either valve will work, but the 3/8" will experience a lesser pressure drop.
I am a bit leery of the 1/4" valve's 4,8mm DN.
H-800.pdf