Walter Knoll Berlin Chair - missing bolt  

Hi all,

I am new to this forum and was hoping if someone is able to help me with the following: 

I recently bought a Berlin Chair at a sale of Mr Design ( https://www.misterdesign.nl) and after a while I noticed that a bolt was missing in the bottom part of the chair (causing the chair to squeak upon sitting on it - it only started doing so after a while, see attached photo). Unfortunately, Walter Knoll can’t help me with a replacement (of the bolt apparently) or help me any further as the chair is out of production. So my question is, would anybody have any idea of what type of bolt it is and/or if there is any way to fix this myself? If not, and if I don’t find a way to fix this, can anyone perhaps tell me if this will eventually damage the chair?

Thanks in advance,

Erik