Pneumatic cylinder details?

What is the thread size and pitch for the end of the pneumatic cylinders? I need to order some additional nuts as they tend to go missing.

The ends of the double action pistons are #6-40 (diameter #6 thread 40).
Not sure about the single action pistons, but they SHOULD be the same.

The rod of a VEX pneumatic cylinder is #6-40. Here’s some: McMaster-Carr

Single acting and double acting cylinders are the same.

Cylinders refer to the whole device, I’m specifically talking about the piston rod, sorry if I was a bit unclear.

You were perfectly clear: it’s just a pet peeve that the VEX community refers to pneumatic cylinders as “pistons.” (it’s no better in First, where they call the little DC motor a CIM, which is just the acronym of the Chinese factory that makes them). In my real job I design a lot of pneumatic and hydraulic equipment, and I’d probably be fired for incompetence if I ever started calling cylinders “pistons”!