In blg, every item is linked to its stock management.
Basically, a part will be managed under "classic" stock management, a labor or transport under "non-stock management", and a material (with serial number) under "material" management.
When you indicate on the item master record that it is managed in "material" stock management, this means that the item will be linked to its material model (range/brand/model name) and also to its material file from purchase to sale.
On the item file, If you click on the material management, the model field will appear to be filled in.
If the template does not exist in your database, it can be created by clicking on "Create model" :
Enter its range, brand and model name, then click on "Save" :
Note that each item associated with its stock management also depends on its nature.
If the nature of the item does not correspond to its stock management, blg will indicate an error.
Example : an item of labor type in material management :