The SANWA LB-35 Balltop is a standard across most Japanese Viewlix arcade machines, and used in almost all commercial joysticks. 
The 35mm size ball top fits Sanwa JLF-TP-8T and JLW-TM-8 and all Seimitsu joysticks.  It's great for those who want an authentic japanese joystick feel, and control using their fingers rather than the entire palm.