Can't really see from your picture but they will probably be countersunk Torx set screws. Just try an ordinary bolt to get the thread size, most likely M8 with a fine thread.
Thank you guys. I took the one from the other door and measured as advised (so obvious, why I did not think about about it myself :-)
I ordered 8x12mm COUNTERSUNK CSK ALLEN SCREW BOLT from eBay and it is a good fit. http://www.ebay.co.uk/itm/261720162491?_...EBIDX%3AIT