Unit of Measures

Hi , One of the sub BOMs are to be bought in ‘set’ UOM which equals to 3 ‘pcs’. How to set this in axapta. What is done Scenerio 1) just insert UOM as set and attached this to item in item master quantity tab. Do we need Scenerio 2) Do we need to have item unit conversion and relation with set to pcs. What exactly system does in the above two scenerios.[?] Any help or suggestions are welcome. Thank you, Kind Regards,[:)] Manjushree