Firmer chisels
The edge that cuts a mortise clean and pares a shoulder square.
The firmer chisel is the workhorse of the frame — thick-bladed, meant to be driven with a mallet, and sharp enough to pare a mortise wall to a mirror.
The set
1/4" — 1" widths, for mortises and shoulders firmer rectangular cross-section, struck not pushed paring long and thin, for the final clean-up bevel 25° grinding, 30° honing
Care
Back the iron flat once, keep the bevel touched up on a stone, and it'll outlive the bench it sits on.