When using a pricking iron, the traditional technique is to tap the prongs only slightly into the leather, and to completely puncture the leather with an awl during the stitching process. With this technique, it is very difficult to achieve perfectly aligned stitching on thick edges. However, there are alternatives to this technique. One method is to use a japanese style pricking iron which is designed to punch completely through the layers of leather. These irons differ from traditional irons in that the prongs are not tapered. If you were to try to punch through all layers of a thick edge with a traditional iron, your holes would be very large. This is because the prongs become wider as you go deeper.
Another technique can be used to produce perfect stitching patterns on both sides, and still use traditional irons. Here is how:
1) Mark a stitching line with a compass on the front and back of the edge.
2) Prick on the stitching line on the top side of the edge.
3) Every inch or so, push an awl through a stitch mark. Only push far enough that you can barely see the tip come through the other side.
4) Turn the piece to the other side and mark the stitching line with an INVERSE pricking iron. These irons have teeth moving in the opposite direction as a regular iron, and will be aligned with the stitches on the other side. As you mark the stitching line, use the awl marks made in the previous step as a guide to ensure that your stitching pattern is aligned with the marks on the opposite side.
5) You now have perfectly aligned holes on the front and back of the edge. Stitch the edge as you normally would.