I just looked at 5 of these, there are slight differences.The closest one is on a 4.2PE with a red anodized case..The casting numbers on the base are 49ZN4 W2+ MAHLE....The cylinder extension at the base is machined flush and the transfer ports are opened straight down to the size of the hole in the crankcase...The bore and stroke is the same for all, so any cylinder you find should work...Air Hobbies used this same cylinder, I have one here....The Air Hobbies cylinder was not machined flush or ported like the PE....