What you're holding
The ABB 1SAZ721201R1043 is a thermal-overload heater element from the 1SAZ721201R family — a snap-in resistive module that lives inside a motor-starter overload relay and trips the auxiliary contact when sustained current heats the bimetal past its trip curve. It sits in the Thermal Overload Heaters for Starters sub-category under Contactors and Starters, so the buyer already knows what they're spec'ing it against — a heater pack matched to a particular amp range on a given ABB overload base.