I started to notice a pattern after a while - all the "M" sticks were the round handles.
All the "E" sticks were the flattened curves.
The "E" sticks came in two versions also - - some with color coded tips, and some with squished flat ends. - -
There were W's and circle B's - - there were a few more markings that I have seen....
Those are the manufactures designation code - I would think???
I believe they were all being used interchangeably - - the wording on the sticks is what was consistent from year to year.
Also the length, and full markings - remained constant for the different applications...
As the GM recommended oil quality changed - so did the wording on the sticks.
Yes - I got to know a lot of dip sticks over the years