FISCH
Premium brand of Austrian made hollow chisel & bit sets.
Note the collar mounting diameters of 15.88mm and 20.64mm are an inch size due to the wide adoption of these dimensions in the metric world
Ø = the width of the mortice
NL = depth of cut possible
GL = overall length
S = the diameter of the shoulder of the chisel
S1 = the diameter of the shank of the drill