What is a Nikon "K" lens?

[reddesert]

But this Rockwell table I find confusing at first sight. I mean, he calls a sample "Non-AI", but it got already those prongs.

Or had the lenses for the very first Nikon F already prongs to couple with that stick-on meter?
I ask as nobody corrected what I wrote above.

Yes, you're confusing the silver prong for non-AI coupling on top of the aperture ring, with the black projections at the rear of the aperture ring for AI coupling. What you wrote above is incorrect for practical purposes. I don't know if the very first Nikon slr lens included the silver prong to couple the meter, but for practical purposes, even first generation Nikon slr lenses do all have the silver prong, unless it has fallen off.

This photo shows the two couplings on an AI lens. On a non-AI lens, the aperture ring projects back a little further, there is no black tab, and the silver prong is solid without holes in it.

 

[mohmad khatab]

Here are a few:

http://www.aohc.it/index.php
http://whitemetal.com/pentax/
http://kmp.pentaxians.eu/
https://www.pentaxforums.com/lensreviews/
https://takumarguide.weebly.com/takumarology.html

https://www.pentaxforums.com/forums/ is a great source of information on all things Pentax.

You are a good man from Florida.
Thank you very much my dear brother,

 

[Disappointed_Horse]

You are a good man from Florida.
Thank you very much my dear brother,

You are quite welcome my friend!