Designed to provide an easy connection to hose ends, these Proflow AN Transmission adaptors allow you to use AN hose fittings.
Note: Ford C4 transmissions were produced in the USA from 1964 through to 1986 (Later boxes were actually renamed as C5 )
Majority of C4 transmissions have/use 1/8 NPSM trans cooler line fittings but later boxes were 1/4 NPSM for this reason you will need to check what thread size you have
The term C9 and C10 is not recognised in any USA literiture, as its a Australian slang term to identify particular C4 gearboxes
What we call a C9 is case fill 26 spline C4  What we call a C10 is a pan fill 26 spline C4