John Guest reduces straight from hose dimension 9.5 mm to 4.7 mm which corresponds (3/8" x 3/16")
Can be used in conjunction with restriction hose to reduce the flow rate of beer when draining when missing beer tap with flow control.
These couplings are completely interchangeable with couplings from affordable Fluidfit, these can be found under accessories.
To find the right one, you can start from this table. Keep in mind that it can hit up to 5 mm when measuring over threads so it is not accurate but indicative.
R - Inch - Inv thread - Utv thread
R6 - 1/8" - 9mm - 10mm
R8 - 1/4" - 12mm - 13mm
R10 - 3/8" - 15mm - 17mm
R15 - 1/2" - 19mm - 21mm
R20 - 3/4" - 24mm - 26mm
R25 - 1" - 31mm - 33mm
R32 - 1 1/4" - 39mm - 42mm
R38 - 1 1/2" - 45mm - 48mm
R50 - 2" - 57mm - 59mm
R65 - 2 1/2" - 72mm - 75mm
R80 - 3" - 85mm - 88mm
R100 - 4" - 110mm - 113mm
