Given that swapping out pushrod can be a real pita, this may be info for the next plane. The red Sullivan rods are usually labeled as "flexible". The general intention is that they are useful when you have to snake a rod around other structures or go around a curve. I generally use them for throttle linkages and small airplanes up to about .25 engine size. The blue "standard" rods are much stiffer. The stiffness comes more from the sleeve then the inner rod. I would have to go out to the shop and check but I'm pretty sure that the inner rod from a blue sleeve wont fit in a red sleeve.