A JF6 is a two lidded footway box.
The others, quite possibly, different varieties of the same.
I dare say poster MC31 may have the complete answer.
Here what I have always believed but don't know for a fact so would be good to have it confirmed/denied
JF6 = is the frame and cover for a 1310X610mm chamber but not the chamber itself.
JMF106 = is a modular 1310X610mm chamber in 150mm sections (character after 106 determines depth e.g. c=750mm d=900mm) but not the frame and cover.
JBF106 = is a brick built chamber (character after 106 determines depth e.g. c=750mm d=900mm) but not the frame and cover.
Edited by deleted (Sun 05-Jul-20 22:17:18)