Movement allowed:
- a 20 mm: Smooth rubber 8 mm. (+/-4 mm) / 5/16″ (+/-5/32″) // Grooved rubber 10 mm. (+/-5 mm) / 3/8″ (+/-13/64″)
- a 30 mm: Smooth rubber 10 mm. (+/-5 mm) / 3/8″ (+/-3/16″) // Grooved rubber 12 mm. (+/-6 mm) / 1/2″ (+/-15/64″)
- a 40 mm: Smooth rubber 12 mm. (+/-6 mm) / 1/2″ (+/-1/4″) // Grooved rubber 14 mm. (+/-7 mm) / 35/64″ (+/-9/32″)