filter thread?

It's quite a pain to remove or attach a filter to your lens because they are using threads, I often wonder if it would not be easier if they use a bayonet instead.
It would probably never happen because almost every one use the same method to attach a filter and the products available for it is enormous but we can always hope right.

Are there maybe other reasons why to use a thread instead of a bayonet?

Size, simplicity and compatibility.

The thread method is simple and does not require any additional specialised tooling. Threads are standard worldwide and not covered by patent or copyright.

The threaded portion is quite thin and adds very little to the overall dimension. A bayonet would be bulky in length and diameter.

Compatibility - most lenses use the same thread family so you can easily move your filter from a Pentax lens to a {censored} lens to a {censored} lens.

First two aren't the problem it's the last one that's the deal breaker.

Just look at the way most lens hoods are attached, the functional bit is just as high as the filter thread inside, it's only slightly thicker though but I'm happy to trade in 2mm to make it easier and faster to remove the filter.
And bayonets aren't so keen to get stuck like thread can do and also sand or other dirt would be less of a problem.

For compatibility, I can't see why B+W or Hoya (maybe together) can design one and submit it to make it into an ISO standard.
Some lenses mostly in the range of normal focal length and above might be able to use adapters?
For wide angle lenses though it might be a problem.

Still it needs to be adopted by lens makers and that might be a problem...
Still lens mount also went from thread (m42) to bayonet (k-mount) so it can be done.

This has been done in the past, when most makes of Twin Lens Reflex used Rollei bayonet fittings, usually in sizes 1, 2 or 3.

They could design one but getting adoption. No chance. Lans manufacturers would want to see a full range of filters before committing a new range of lenses to it. Hoya and B+W would want to see lenses in preproduction before they start manufacture. They would then have to run a double production line for many years to supply existing lenses and those who would not change.

Lens mounted changed - but how many difference types of those are aound?

Too bad it didn't catch on John.
Strange actually...
In the time when B&W film was popular (sixties?) some people surely would have thought that a thread takes quite a lot of time and fiddling around when switching colour filters, or white balance filters for colour film.

Well Hoya has Pentax and have Tokina as a good friend.
B+W is part of Schneider and they also have Pentacon/Practica.
As you know Samsung lenses are sold under the Schneider name so they at least have some connections with each other.
They could make an adapter for their lenses so that you can still use threaded filters so it wouldn't hurt the lens sale.
I can surely see that if B+W and Hoya make the jump to make a bayonet filter that soon others will follow.

Have a look at a Rolleu filter Stefan and see forsty how small it is and then how highly engineered the bayonet is. Not just a simple turn and click like modern ones, but high grade steel and ball bearings and springs....

To make something like in in say 67mm fit would result in a lens hood costing several hundred pounds.

Does the Pentax 67 not have bayonet filters?

I had a quick look when you mention it John, didn't saw that it was so complex
A simple turn and click like a hood looks like it should be enough. At least I never had a problem that a hood become loose or anything like that and a hood is heavier than a filter.

Just dreaming here though.

I believe so, but I've never examined them closely. They are horribly expensive!

Looks like thread to me link but I can be wrong.

As someone who's owned a few Rolleis I have to say their bayonet filters (both the TLR and system camera varieties) are a joy to use - massively over-engineered (like everything Rollei used to make) but deeply satisfying. The down side is that they cost an arm and a leg and they don't do anything a regular screw-in filter won't, hence I'm happy to settle for a little loss of convenience these days in return for large savings in cash and easy availability...