I recently had a problem with my cylinders on my SM L-39. They leaked and when I tried to pull the airlines off to replace them, two nipples came off one main cylinder. As replacements, I tried the Air Power 1 1/2 stroke 3/16 dia and they were not powerful enough to keep the doors closed. The UP 1 1/2 stroke 7/16 dia is what I ended up ordering from Dreamworks. The flight loads are what you have to watch out for.