They are strongly constructed with a single-sided straight edge, resembling a small cleaver.
Unusually for an axe, this back edge is intended to be hit with a steel hammer, not a wooden mallet or club.
The hacking knife is used to chop out old putty before replacing glass panes.
The side knife may be used as a light froe, for splitting small billets of wood.
Unlike a froe's extended handle, the side knife does not permit twisting to lever the split open and so it must be driven through all the way.