Yes these are for the Crawford 5C collet chuck that operates with a chuck key just like a normal 3 jaw chuck.
Because they put the bevel drive the wrong way you need LH threads to tighten the collets.
They are also a courser pitch to make up for the low gearing.

If you have a set you are lucky as they are as rare as hens teeth and mega expensive.

I have a Crawford collet chuck but I replaced the threaded nut with a home made one to take normal 5C collets,
OK it goes the wrong way but you soon get used to it.
I only had 3 collets for mine and this was the easiest way to attack the problem and use my existing set of normal 5c's, I sold the spare collets on Ebay and got a decent figure for them.

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