I encountered that limitation early in my use of Inventor and decided to make my own Mark No.
It is a composite number consisting of Custom iProperties: "SHAPE" + "MARK", or whatever you need.
Then I use the Inventor's native "Stock Number" to construct the part's Mark No: =<SHAPE><MARK>, or just =<MARK>. which shows up as a letter & number or just a number (depends on type of project). This occurs as an iProperty in all my ContentCenter parts, so the drawing PartsList automatically populates.
Example: Pipes are "P01" (etc.)
Beams are "B01" (etc.)
Weldments are "W01" (etc.)
Concrete is "C01" (etc.)
You can make it anything you want, with as many place holders (iProperties) that you want.
Or, if you want to make a string of numbers that shows model structure, you can use iLogic to string together all the "MARK" numbers, separated by a "." (dot). But you have to be sure you don't over-write a number that you already created of a part that exists in a previous sub-assembly. That's where it gets tricky, and you have to decide on what rules you will use to do numbering. Numbering is never easy if you are in a complex modeling environment.
I do all my numbering manually. But if you can make an iLogic rule, maybe you can automate the numbering process?
... Chris
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