Threshold is related to Limit. Limit is related to Edge. Shoulder is a type of Edge. Shoulder is related to Hand. 
Bath can be used for Fill. Bath is a different concept from Shower. 
Threshold <--RelatedTo--> Limit <--RelatedTo--> Edge <--IsA-- Shoulder <--RelatedTo--> Hand 
Fill <--UsedFor-- Bath <--DistinctFrom--> Shower 