50/64 indicates the choke setting.
50/64 means equivalent orifice diameter in 50 times of 1/64ths of an inch.
Following figure the indicator is at 42 this would be equivalent to an orifice bean size of 42/64.

Choke valve manufacturers have generally have Orifice Indicator Bean Sizing Table and/or choke setting vs. Cv diagrams.
Reference: http://www.diwmsi.com/flow/chokes.asp