SD/ OD Transaction
I'll explain with an example.
a).Create an Item with Primary UOM as GA and Purchasing UOM as LB.
b).Create the UOM conversion between LB and GA. Say 1 GA=5 LB
c).Create a OD version with the processing option set to default the Purchasing unit of measure which is LB.
d).Let the SD version be set to default the primary UOM which is GA.