Stew Mac fret saw and fret slot width problems!

Typical fret wire has a tang width Rounding to allows a max tolerance of 12 tang width OK for me; don't know about you

But StewMac recommends a slot width of for both sizes of fretwire The medium fretwire goes into the slots with what seems like

fret slot width TL07 Fret Slot Saw £ Stiff backed with wooden handle, dressed for fret tang width

fret slot depth TL07 Fret Slot Saw £ Stiff backed with wooden handle, dressed for fret tang width