Sic,
The original RAM 750 pump (circa 1999) had Festo fittings instead of barbed fittings.
The pump inlet fitting WAS 6 mm, and the outlet was 4 mm.
When Hausel came out with their pump, everyone including RAM jumped on the bandwagon with them. Considering the price of the pump, it's cheaper to buy them O.P. than to make them in house.

Attached are a couple of photos of the original RAM pump and it's new home on my "Montana Modeler" fuel can....14 gallons, from Pep Boys Auto Parts....around $100.00 before conversion. On 4.8 volts, it fills a KingCat about a minute slower than the original pump on 7.2 volts (the type Jersey Modeler uses, and creates far less static imbalance as well).
When I switched to the old RAM pump, 90% of the static charge imbalance problem went away.
No flaming intended......
As you can see, the pump has a 6 mm inlet fitting. I wish they were still made this way too.

Harley Condra
BVM REP
JetCat REP