FS-2E series size 42/21/20 ferrite transformer bobbins with insulation according to class B and flammability to UL 94 V-0. These ferrite transformer bobbins are available as horizontal (stock number 840-7282) or vertical (stock number 840-7288) mount. Typical applications for these ferrite bobbins include transformers and inductors in switch mode power supplies.
For ferrite cores please see stock number 840-7153 typically

Transformer Ferrite Kits - Cores

The A_L value in the table applies to a core set consisting of two cores without air gap Cores ETD conform to IEC 51(CO)276