It can be a good idea to create a special catalog where only stock sheetmetalshapes are stored.
-Create a sheetmetal stock.
-Adjust the thickness to the smallest you like to work with.
-Drag that shape in to a new sheetmetalcatalog.
-In the scene, change the thickness to the next that you like to store.
-Drag that shape in to the newly created catalog.
-Continue with this for all of you popular sheetmetal thickness that you like to have.
Now its more easy to change the thickness when you start to create a new sheetmetalpart.
-Remember that you can CTRL-drag from catalog to repace existing parts in the scene.
-You may want to check where the anchorpoint is located on the stock, before dragging in to the catalog.
-All selectable sheetmetal thickness values are stored in the databas file "tooltbl.txt" in the folder "Common"
The easiest way to add rows in tooltbl.txt is to copy one existing row, paste it in, and change the values.