“Righty, tighty Lefty loosy.” is a common axiom to help remember which direction tightens and which direction loosens a screw, nut, bolt, etc. To  tighten, you must turn it to the right (clockwise).  To loosen it, therefore, you turn it to the left (counter-clockwise).  The adage works ALMOST all of the time….except when there is a “reverse” (or left-handed) thread.

Reverse threading is often used in rotating machinery where the natural motion might cause a right-handed fastener to unscrew.  For example, the left pedal on a bicycle is left-hand threaded while the right pedal is right-hand threaded.

You might be surprised to learn that all R-1234yf cylinders, cans and dispensing equipment are actually “Righty, loosy Lefty tighty,” or reverse threaded.  We frequently receive phone calls from frustrated consumers who cannot get their R-1234yf accessories to screw on.  Although there is no danger of the dispenser to inadvertently unscrew, these reverse threads are intentional to prevent accidental contamination with another refrigerant or gas.  So it is impossible to use an R-134a can tap on a R-1234yf can.   Mixing refrigerants can cause unpredictable changes in the pressure-temperature relationship.

Note the “LH” etched into the side of FJC’s R-1234yf can tap Part # 6840 (it stands for “Left Handed” thread).

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