Glossary
Stitching chisel
A pronged punching tool that drives all the way through leather in one strike, cutting the holes a saddle stitch is sewn through.
A stitching chisel looks similar to a pricking iron but is built to punch completely through the leather in a single mallet strike, cutting clean diamond or slit shaped holes rather than just marking the surface. It comes in various prong counts, letting you punch several stitch holes at once in a straight line.
Because it cuts all the way through, a stitching chisel is generally the faster and more beginner-friendly option for preparing stitch lines on medium and heavier leather, especially compared to relying on an awl to punch each hole individually. The tradeoff is that the holes it leaves are usually a bit larger and less subtle than a fine pricking iron's marks, which matters more on delicate, thin work.
Match the chisel's spacing and prong width to your leather weight and thread thickness, since holes that are too large leave loose, sloppy looking stitches and holes that are too small make pulling thick waxed thread through difficult. Keep the chisel square to the leather and strike it straight down, since a common mistake is angling the tool, which produces crooked holes that throw off the whole stitch line.