When Products are purchased... you can setup a minimum quantity and a maximum quantity as well as the units that they must be ordered in ...
- Minimum - the minimum number that you can buy for the product (Default = 1)
- Maximum - the Maximum number that you can buy for the product (Default = 0-Unlimited)
- Units - the increment qty that you must buy the product (Default = 1)
If you make it so that the minimum quantity was 12 but had to be ordered in units of 3, then the allowed quantities would be:
12, 15, 18, 21, etc.
These have nothing to do with product quantity "In Stock". ... Inventory On Hand (Stock) is handled by the "Product Quantity" field elsewhere on the same screen.