I haven't tried the ultimate, but the Ms. Pac-Man/Galaga replacement stick is identical except for the length and style of the shaft, and the bottom plate has a diamond-shaped restrictor hole. All other parts are interchangeable, and the mounting plate is exactly the same size. I would assume that most of the Happ sticks share the same base, just with different restrictor plates and whatnot. Try looking at the exploded/mounting views on the Happs site for measurements.