On Z-shaped offset (1) features, try to keep all the bend radii the same, with 0.030 in. the preferred radius, and parallel planes should be at least two times the material thickness apart. With holes and slots (2), place at least 1/16 of an inch from the nearest wall or part edge for materials 0.036-in. thick or less, and 1/8-in. or more from the edge on everything else. Tabs (3) on either side of a notched feature should be at least 0.126 in. or two times the material thickness across (whichever is greater).
Also, keep in mind that metal resists bending. To prevent cracks and meet a +/- 1-degree bend tolerance, Protolabs will place bend reliefs in strategic part locations—with a box shape, for example, the corners will be relieved slightly to allow the flanges to meet properly. The total amount of bend relief in this case will not exceed the bend radius plus the material thickness, and be no wider than 0.030 in.
Offsets are Z-shaped bends that might be used on brackets and clamps—the clips that hold your window screens in place are a good example. The same rules apply here as with any other bent part—try to keep all the bend radii the same, with 0.030 in. the preferred radius. Also, the parallel planes should be at least two times the material thickness apart, and you can expect Protolabs to maintain a tolerance of +/- 0.012 in. between the two features.
Bend a flange all the way over and you have a hem. They are used to strengthen part edges. An open hem is one that forms a U or C-shape and might be used to accept a pin for a hinge. Closed hems are basically flat, with the material folded over completely on itself. The inside diameter of an open hem should be equal to or greater than the material thickness, and the “return length” in either case should be at least four times that.