Sierra is the shortest as said, I think if you are looking for a generic size that would fit "most" pen kits I would have to say about 4 1/2 inches will be enough to build most two piece pens. Keep in mind though that this wouldnt take into account cutting the center band out of the blank for grain alignment and such. Even with taking that out 4 1/2 will still work for most pen kits that I have measured.