ST style.  For example, RSM has them, Randy Smith PA has them.

     Hello All:

     It is time for me to make large purchase of nva.  My question is: which type should I buy?  Should I choose the flexible OS/Enya style or the rigid ST style?

    The OS style can be made rigid just by soldering up the spring, if you want. I much prefer that type as far as the way the needle is controlled inside the spraybar, it's much more stable than the ST type, and they have click stops, which for many cases keeps you from screwing around with too small a change.

    The other real choice is the PA/Jett types, they work about the same, although the Jett is larger. Those are also far superior to the ST, or the ST clones and not nearly as prone to the "tuning fork" effect that the original or rip-off ST style.

   As noted, many of the ST clones are very poorly made and some of them don't work at all.

   Of course,  engines come with needle valves, so use those, or identical replacements, if you have them. 

     Brett

The "ideal" click number per revolution is directly related to Threads per inch and taper angle. Finer threads and/or longer more gradual taper will need less clicks per revolution than the opposite to make one or two clicks result in a reasonable change in flow.. If it's strictly for suction feed on a stunt engine the ideal will be vastly different from a high performance engine on pressure. A lot of the cheap aftermarket needles had sloppy thread fits and poorly ground tapers, both of which cause inconsistent adjustments and vibration induced problems. If the threads and the taper are not concentric the adjustment may not be linear. sloppy threads result in air or fuel leakage and the symptom of instant Setting change from just touching the needle (before you actually turn it) Randy's PA NVA's are very well made and have nice linear adjustment range with a nice Delrin or Teflon seal that gives proper drag without binding. The Brodak NVA's work very well for the medium size engines (width wise) and the collet nut clamps the needle on the smooth unthreaded portion of the needle which creates smooth clamping drag without binding or wearing the threads. With The PA or Brodak NV geometry, clicks similar to the OS or slightly finer should work well. Too fine still works; Too coarse doesn't