In conversation with a fellow member I was asked the differences between Mk1 & Mk 2 Ajax's, 1933 to 1946, not exactly sure when the change from Mk1 to 2 was but I believe possibly 1936.
On quick inspection they look very similar, however a closer look reveals the following differences Mk 1 first & Mk 2 in brackets.
Smooth rear roller (Ribbed)
Front single wooden roller with screw in shafts (4 separate wooden rollers sliding on shaft)
Cutting cylinder 3 supporting webs/spiders (4)
Wooden Handles threaded direct to flange (Flange & fixing modified)
Holes for oiling (Nipples)
Cylinder adj single bolt (Lock nut added)
The Mark 3 of course introduced the alloy sides & during production the move from straight to cross-over handles.
I will leave another to compare the 3 with 4 & 5 as none in stock at present to compare.