Manufacturing defect
The holes in the rod and the pivoting coulter do not coincide when the coulter is placed in abutment on the rod. The 10mm bolt that holds the coulter therefore does not fit. You can make the holes coincide, but then the coulter is no longer in abutment and it is the bolt that will support the effort, which can be very important. The thread will inevitably be damaged and the bolt will twist. With the risk of no longer being able to remove it. I was able to solve the problem by putting in a 6mm bolt and washers. The coulter is then firmly in abutment. And, in this case, the bolt does not undergo any effort and 6mm is enough.