Hard wheels (wheel size/barrel size in mm)
50/27 barrel
50/36 barrel
50/38 barrel (heavy or regular duty)
50/38 barrel, Auto-Lock*
50/45 barrel, Sit-Lock*
50/45 barrel (heavy or regular duty)
55/38 barrel
55/45 barrel (heavy or regular duty)
60/38 barrel

Soft PU wheels (wheel size/barrel size in mm):
50/27 barrel
50/36 barrel
50/38 barrel (heavy or regular duty)
50/38 barrel, Auto-Lock*
50/45 barrel, Sit-Lock*
50/45 barrel (heavy or regular duty)
55/38 barrel
55/45 barrel (heavy or regular duty)
60/38 barrel

Hard wheels (wheel size/barrel size in mm):
55/33 barrel
55/38 barrel
55/45 barrel
60/28 barrel
60/36 barrel
60/36 barrel, Auto-Lock*
65/18 barrel
65/22 barrel
65/25 barrel
65/36 barrel
75/36 barrel

Soft PU wheels (wheel size/barrel size in mm):
55/33 barrel
55/38 barrel
55/45 barrel
60/28 barrel
60/36 barrel
60/36 barrel, Auto-Lock*
65/18 barrel
65/22 barrel
65/25 barrel
65/36 barrel
75/36 barrel

*Auto-Lock = wheels will resist rolling when not seated.  To prevent chair from rolling away causing personal injury.
*Sit-Lock = wheels will resist rolling when seated.