tractor turned out great give youselves a pat on the back
the zt series beginning 1936 used the new mm engine on the old twin city j rear end with hand clutch
the za series beginning 1949 had mm designed back end still with hand clutch
the zb series beginning 1953 used the foot clutch finished up by 1955
the third letter gives the front wheel style s- standard, e- wide adjustable, n- single front wheel, u- two wheeled narrow front, i- industrial
this applys to the z, u and g (only available as a standard) the r remained an rt right through the production of them