Screw fitting is 1/4 "X 40 TPI.Pipe connection for the 3MM. he main hole is 3.5mm. Technology and ability to operate So we hope that you must understand before buying.
Reversible Control Valve for Live Steam Engine with 1/4 x 40 TPI Fitting
Reversible control valve for steam engine model Screw fitting is 1/4 "X 40 TPI
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
