Does anybody know what a stall strip is? How is it used?

From Wikipedia:

A stall strip is a fixed aerodynamic device employed on fixed-wing aircraft to modify the airfoil used. They are usually factory-installed or, on rarer occasion, an after-market modification. Stall strips are almost always employed in pairs, symmetrically on both wings. In rare installations they are employed as a single stip on one wing to correct aberrant stall behaviour.

A stall strip alters the wing’s stall characteristics and ensures that the wing root stalls before the wing tips. This is usually as a result of initial aircraft flight testing which shows that the existing stall characteristics are unacceptable for certification.

In some cases, such as the American Aviation AA-1 Yankee, stall strips are planned to be used on the wing from the start. In the case of the AA-1 the left and right wings were identical, interchangeable and built on a single wing jig, thus the more traditional use of washout in the wing design was not possible.

Stall strips can be an alternative to washout in aircraft design or they can be used as well as washout to improve stall performance.

Stall strips typically consist of a small piece of material, usually aluminium, triangular in cross section and often 6-12 inches (15-30 cm) in length. It is riveted or bonded on the point of the wing’s leading edge, usually at the wing root. Here it acts to trip the boundary layer air flow at higher angles of attack, causing turbulent flow and air flow separation. This has the effect of causing the wing root to stall before the outer portions of the wing, ensuring a progressive outward stall and aileron control through the stall.

EDIT// By the way. Very good question. I learned something too

http://en.wikipedia.org/wiki/Stall_strip
Not really all that effective in models.

The above explanations are fine as to the theory. The only one I had experience was on the old USAF T-33. It assisted in spin recovery, plus made the spin entry more predictable. They were a very rough addition of simply about 18" ( I don't really remember exactly) of angle-iron roughly welded on to the wing leading edge a couple feet or so outside the fuse / wing joint.

Now about a model! [X(] Once upon a time there was a DEMECO (Hal deBolt) model called "Cobra II". Designed for a very old event called Formula II Pylon Racing, with a .40, it made a great sport model with a .50-61 engine.
After a few flights with that machine, I entered a spin. SURPRISE! It went into a beautiful FLAT spin, from which I could not recover. I tried everything I could think of using power and flight controls. It spun right down to the ground, and that trike gear just sat down very politely with the engine at idle, ready to go again. I just had to do that a few more times. On about the 5th or so spin-in, I did finally break a prop.
Then I remembered that old T-33. I rigged some 1/16 x 3/8 x 3" (Size determined by TLAR -- "that looks about right" ) ply strips, made my "angle iron" and glued them about 3" out.
That Cobra then spun very well, easy to recover and just very normal. I removed them once to make another test. Flat and unrecoverable again. Strips back on and all is well again.

I could never figure it all out as others never had such a problem. Must have been a building error on my part, however it was fun. In that model stall strips worked exactly as advertised. I still have another kit. Maybe some day ..........???

simply put..small trianglualar pieces of metal on the leading edges of the wings to increase the speed at which the inboard section of the wing stalls.....thus eleminating or decreasing a tip stall...or to help in spin recovery