vacuumkid47
Logan,
It means the 510 was produced from 1950-1951, and the 511 from 1951-1952.
There was a change to the front bearing assembly during production of the 511. On units at serial no. 383346 and earlier (and all models 3C to 510), there is no provision for relubrication of the front bearing; if defective, replace both the bearing and the bearing plate. Model 511s made at serial no. 383347 and later have a removable front bearing.
~Ben
