FS-1ETD series size 49/25/16 ferrite transformer cores made from N87 with a cylindrical centre leg. These ETD ferrite cores are available with air gaps inserted:
Stock number 840-7424 has a 0.1mm gap
Stock number 840-7507 has a 0.2mm gap
Stock number 840-7594 has a 0.5mm gap
Stock number 840-7676 has a 1.0mm gap
For bobbins see stock numbers 840-7364 and 840-7367

Easy compilation of components for pattern construction

Typical applications for these ferrite cores include transformers and inductors in switch mode power supplies.

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