FS-1ETD series size 29/16/10 ferrite transformer cores made from N87 with a cylindrical centre leg. These ETD ferrite cores are available with air gaps inserted:
Stock number 840-7415 has a 0.1mm gap
Stock number 840-7496 has a 0.2mm gap
Stock number 840-7579 has a 0.5mm gap
Stock number 840-7667 has a 1.0mm gap
Typical applications for these ferrite cores include transformers and inductors in switch mode power supplies
For bobbins see stock numbers 840-7339 and 840-7333
For potting box see stock number 840-7406

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