A student should be 6” CH a master should be 6.5” CH
Having said that apparently colchester made most students 6.5” without changing the badge which states 6”
Masters were always 40 “ Between centres rather than 24 for the student
Its also a mk1 as it has the sliding handle for cross and longtidunal feed
Mk 1.5 ‘s have a lifting knob and a separate knob to cross and long
Mk 2 would be square head