What are Oleo's? I'm going to replace the retracts in my H9 Miss America P51 60 size with Spring Air retracts. But I was asked if I wanted OLeo's. ????

AJ,
These are the compression struts in the gear. The other choice is heavy wire struts which are not scale. The oleo is a tube in a tube with a concealed spring that lets you get away with a less than perfect landing.

Oleos will allow all the force from the bad landing to gather power from the compression of the springs within them. One of two things happens at this point; the plane rebounds like Michael Jordan (BOINGGGGGG), or the landing gear explodes through the top of the wing
All that said, they are cool, and will work out better than straight wire, or even wire with a coil spring.

A Oleo strut is actually a hydraulic cylinder with a orifice that controls the fluid flow around the piston to cushion shock forces. A spring strut is just that: a spring that cushions the shock force.