Unknown Collet

Does anyone know this kind of collet?
It has 10 ° angle,( 20 ° taper)
The ER collets are 8° ( 16° taper)

If that drawing is correct, in particular the face detail showing a square shoulder and flat face, it's some flavor of "push-out" collet, probably a lathe spindle collet. If that drawing is not accurate, who knows?

I just want to know if these collets exist
Because i have a spindle with a 20° taper and i need collets for the spindle
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Tell us more. Tell us where you got this spindle, and what you were told about it. Show us a picture of the spindle, the machine it came from and especially any labels the machine has. Do you have any accessories that went with the machine like a draw bar, other parts of the collet assembly, chucks, etc. Any information you can provide will aid in identification. What portions of your drawing are you certain of, and which are conjecture? If you only have a spindle, the included angle can be measured with accuracy. The exact design of the collet such as you show might be less certain from a spindle alone. Your post indicates you live in Belgium. There are or were numerous machine tool manufacturers within 500 kilometers of where you are, and even more within 1000 kilometers. More information is more better.
Note: if this is a double reply, I have had a problem of things not properly posting on hitting the button. I don't know what the problem is. It seems episodic. Edit: It worked.

Machinery's Handbook has a page or two of various collets and spec. chart. If that one is not there, it may be machine specific.

I think the spindle is from a internal grinder, no spindle bore
The collets are not for myself, but for a friend
The taper is 20° (10° angle), biggest diameter is about 24 mm
I've measured the angle with accuracy
The drawing of the collets is from a ER collet, i've just changed the angle from 8 to 10°
See the original drawing below

After removing the rust,I've found some marking on the spindle
It is a very old belt driven spindle from GMN R50680

That drawing looks very much like Acura-Flex Style Collets, except that they are missing the retention groove. Also, I am uncertain of the AF style taper but as I recall it was 11 degrees rather than 10.

It's an old round belt driven internal grinding spindle
Made by GNM R50680
I've modified the inner taper to a taper for ER25 collets

balas or balax collet.... maybe a c-6 or c-8 . sandvik.

balas c-8 collet - Google Search