I thought the Pro saws had a metal crank case and the regulars had plastic. I have an 026 Pro and it has a metal or aluminum case.
The 026 and 026 Pro (and MS260 / MS260 Pro) differ only in the addition of the compression release and manual oiler. All other mechanicals are the same.
The primary difference between Stihl "occasional use" and "pro" models is the style of construction of the engine.
All odd-numbered saws (in the old numbering system) such as the 021/023/025/029 etc are occasional use and employ "clamshell" engine construction. All even-numbered saws (again, in the old numbering system) such as the 024/026/028/036 are termed "pro" models and employ traditional "jug-on-case" construction.
About 10 years ago Stihl revised the numbering system, such that they could append a "series" designation to the end of the model number.
Hence, the 026 became the MS260, which eventually was improved upon and subsequently released as the MS261, and so on.
In the case of the "new" numbering scheme, if the middle number is odd, it is an occasional use saw with a clamshell engine: MS210, MS230, MS250, MS270, MS290, MS291, etc ...
Similarly, in the case of the "new" numbering scheme f the middle number is even, it is a pro saw with a jug-on-case engine: MS260, MS261, MS360, MS362, MS440, etc ...
Wrooster
ps: Since you are now probably wondering, "what's a clamshell engine?", I attach a picture of my little old 021 internals. You will notice that when looked at "end on" to the crankshaft, the crank bearings are captured by two mating pieces: the plastic lower housing and the jug/cylinder casting. When taken apart, the two pieces can be thought of as a clamshell.
