APC 13x4W. It should swing about the same rpm as a MA 12x6. Your ST 60 should swing this prop at just over 12k. My OS 60 FP swings it @ 11,700. My Saito 100 swings it @ 11,000. I had the same plane, and tried with the 13x4W prop on both the 60 FP and Saito 72. Neither is quite enough for hover and pull-out. Your ST 60 should do the job.