a multi - height energy - directing device , for facilitating staged welding together of workpieces . the device includes multiple elements extending from a body , wherein the elements do not all have a same height . each element of a first group of the elements has a first height while each element of a second group of the elements has a second height differing from the first height . the elements are configured to channel welding energy through the device in a pre - determined manner . the predetermine manner includes channeling the energy through taller , primary , elements , of said elements , in an initial stage of the welding process , while passing none through shorter , secondary , elements , of said elements , in the initial stage .