I took it apart today and remembered this. Better late than never. I don’t have calipers but its this big
Fits right in that little spot of aluminum. I’m calling it 17mm x 1.5mm assuming convoy boards are sized right. Picture next to a 20mm x 1.6mm convoy board and a Canadian dime. Little bigger than a 16mm x 1mm board, little thicker. Not quite as thick as a 1.6mm board. So that’s my guess. Maths!