Screw fitting is 1/4 "X 40 TPI. Pipe connection for the 3MM. he main hole is 3.5MM.
Reversible Control Valve for Live Steam Engine with 1/4 x 40 TPI Fitting
Reversible Control Valve for Steam Engine Model P20
P20 Reversible Control Valve for Steam Engine Models – 1/4 x 40 TPI
P20 Reversible Control Valve for Steam Engine Model 1/4" X 40 TPI Hole 3.5MM
Microcosm P20 Brass Reversible Control Valve Compatible with Steam Engine Models
P20 Reversible Control Valve 1/4x40 TPI 3mm Pipe Steam Model
