Because of this there are different considerations given to hem allowances. This will throw off any Bend Allowance or Bend Deduction formulas you are trying to use to calculate your flat pattern. The Inside Setback is only considered in angles up to about 170 ° because as the angle approaches a 180 ° bend the values of the Inside Setback and Outside Setback approach infinity. As you can see these values are heavily dependent on the Bend Angle. The below image shows the difference between the Inside Setback (ISSB) and the Outside Setback (OSSB). The Inside Setback is closely related to, but should not be confused with, the Outside Setback. Because this is a geometrical function it does not change with a metal’s K-Factor the way Bend Allowance and Bend Deduction do. When the sheet metal is bent the inside radius pulls the edge of the material away from the apex of the bend. The Inside Setback is the distance from the apex of the inside mold lines to the tangent point of the inside radius. Understanding the Inside Setback of the workpiece is an important part of designing sheet metal parts.