HLD3600F breakdown
H = High interrupt capacity, in this case 65kAIC at 480V, as opposed to I think 35kAIC if there was no H
LD = 600A maximum frame size
3 = 3 pole
600 = maximum amp rating of the unit within that frame size (can be less than the frame size, but never more, in this case the same)
F = (Frame only), which means it was originally bought with NO trip unit, probably because the soft starter mfr needed something other than standard, or they were buying frames only, then swapping out trip units based on the size of the soft starter.
The point of this was that you will need to look VERY CAREFULLY at what you have and see what the TRIP UNIT says on it! If the F were not there, it would be a 600A Thermal-Mag trip unit, but the presence of the F at the end means we don't know what is on there. If it is a 600A Thermal Magnetic trip unit, it should say LT3600T on it. If not, check with Eaton / Cutler Hammer to see what it is (the numbering has not changed).