The Binocular Core Transformer or twin core

I glued two toroids to make a binocular

A different view of the cores.

 9 turns make 98uh.

The twin toroid and two binocular cores. The cores come in a range of sizes. These are all the same material.

The twin core 1 turn gives 1uh.

 The large binocular gives 1uh. same as the twin core.

 The small binocular gives a little higher inductance.

I wound a 3 turn primary and a 9 turn secondary. The primary reads 4.8uh.

The secondary is 38uh.

So the choices are twin core or a dual aperture. I have wound the large binocular so I will try it next.