Z-XS. Bet nobody else has said this! It's the older style with the small stamp on top and bottom. When they switched to the circle stamp the disc lost all of its glide. Normally, when talking about about discs I will just substitute beat-in P-PD in place of Z-XS because nobody actually knows how the old style Z-XS's fly, which is practically identical to a beat-in P-PD.