FS-2E series size 25/13/11 ferrite transformer bobbin with insulation according to class B and flammability to UL 94 V-0. This ferrite transformer bobbins is horizontal mounting. Typical applications for this ferrite bobbin includes transformers and inductors in switch mode power supplies.
For ferrite cores please see stock number 840-7137 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