Help identifying ferrite toroids

I am going to build a Joule Thief and want to build my own coil. I have a few scavanged toroids around, I want to make use of them (if possible). I guess they are basically ferrite toroids like the once I need for my J.T. but I'd like to have a second opinions since I've never dealt with coils in the past and never made one by myself either.

These are the once (there are more, identical) I'm talking about:

They are approximately 1.5cm (diameter) big. I don't know what they were used for in the past.
Do you think I can custom wire wrap them for my Joule Thief?

What is

Joule Thief

?

What you asking for is difficult if you don't know the specific manufacturer and part number for the toroid. Toroids are made with a specific material recipe, so the number of turns of wire required for a desired induction requires information only avalible from the datasheet for a specific toroid. Also the frequency response of the material can only really be determined from it's datasheet. Same for it's current saturation specification.

Lefty

Magician:
What is

Joule Thief

?

Look at here: Joule thief - Wikipedia

O'K, thanks.
I will vote for core on left side. There is a chance, that EMI choke on right side of the picture isn't a ferrite at all but Iron powder.

These are cool devices. Ever wonder how they are made?

Never mind, and thanks anyway.

It looks like the right one has been scavanged from an old PC power supply.

I used it (I changed the wiring though) and the Joule Thief works, hence I suppose it is of the correct type for the inductor I needed.

hence I suppose it is of the correct type for the inductor I needed.

I doubt it. The efficiency and / or maximum current won't be what it should be with the right core.