What is this for?

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I have no clue, can you wise MNers help?

It looks like a Spirograph piece to me!

Isn't it a spool of thread, just in a different shape?

It is, but what is it used for, why are there two holes?

I should think it likely that the two holes are more to do with the yellow thread being wound onto the piece of plastic in the first place. The piece of plastic probably slotted onto a machine using the holes. I think it's just a 'nice' thread holder for a sewing kit or similar?

Is it for weaving or knitting where you wind thread or yarn round?

I know this thread is a few days old, but ... to me this is the traditional way 'Zwirn' - a sturdier type of thread for sewing by hand - is sold. It used to be cardboard - in the 50ties - now its plastic.
As mentioned above the holes probably have a function in the production process.