The instructions have you mark a center line on the J Stiffeners. This line will be viewed through skin rivet holes to aid in alignment.
I was going to scratch a center line with my calipers but decided to make this little sharpie jig instead. The space between the pen point and wood is 5/16". Just run it down the edge and it marks. Took some time getting this thing made but when it was time to use it I was glad I did. You have 6 10' long J Stiffeners to mark. Went very fast once the pen jig was made.
