F shape laminations are similar in function to E laminations. One notable difference is that the F lamination can be interleaved at the corners of the stack and have a butt stack in the center leg. An air gap can be provided in the center leg during stamping of the lamination. The typical F lamination has a hole near each stack corner. A screw is passed through these holes to secure the stack. If the holes are over-sized a bit, there is some play available. This play can be used as a way to provide some gap adjustment in the center leg by sliding the stacked interleaved lamination a bit. The F shape is not typically found in cores other than lamination stacks.

Core Types Used by Butler Winding