How to read a milling insert code
Take SEKT 1203AFTN. The first four letters work as in turning: S square shape, E 20° clearance, K tolerance class, T countersunk hole with chipbreaker on one face. Then 12 is the size (the side, about 12 mm), 03 the thickness (3.18 mm).
From here milling adds its own positions: A is the main cutting edge angle (45°), F the wiper clearance (25°), T the edge preparation (chamfered), N the hand (neutral, fits right and left cutters).
The wiper edge
The wiper is a small straight flat next to the corner: it runs parallel to the surface and leaves it smooth even at high feed per tooth. In the code it shows as the two letters after the thickness (or after the radius): the first is the main cutting edge angle, A 45°, E 75°, P 90°; the second the wiper clearance, for example D 15° or F 25°.
ISO part and maker's part
After the ISO positions many makers add a dash and their own code: the chipbreaker, the wiper width, a geometry variant. That part is not standard and must be read in the maker's catalogue: two codes identical up to the dash are not the same insert if what follows differs. Some thicknesses too, like the 35 in APMT 1135, are maker notation rather than an ISO code.