help to identify an unknown Fabricius Kastholm office chair  

Hello clavi. Try clicking on...
Hello clavi. Try clicking on the link below and then type RP03839 in the "All Fields" box. Here you'll find a chair by Kastholm & Fabricius that looks really similar to your chairs, however there's a noticable diffence regarding the upholstered seat itself.
http://https://ext.kb.dk/F/-?func=option-update-lng&file_name=find-a&loc...

Error in link
Try the link below instead - and then click on the "Search in Furnitureindex" link underneath the picture.
Knoll might have produced this chair with slightly different seats, however it might also be a replica/copy. Though I'm not familiar with Fabricius & Kastholm's furniture being copied, their work is simply not that well-known.
http://kunstindustrimuseet.dk/furnitureindex/

Incredibly helpful
Thanks a lot for this precious link.
The reference you pointed to seems quite close, though mine doesn't have the shock absorber feature and might be older (maybe more kill than knoll).
Anyway, I will take actual delivery of the seats on tuesday so I will let you know and might post better pictures.
Thanks again
Clavi

Fabicius / Kastholm chair pictures
Finally got the chairs.
I had initially planned to buy one only, and wanted to select the best one from the 3 available, but upon reviewing them I found them in equal condition, and decided to go for the 3 of them...
I thought that keeping the full set together was better than splitting it apart.
here they are. perfect quality of construction and great leather.

Clavi