I split the shafts on my right wing turkey primaries.  
1st: What is the min. width to get good glue adhesion.  I am trying to figure if I can get two fletches out of the longer primaries?

2nd: Advantages to using only primary feather, or do secondary feathers make just as good fletching?

3rd: If I use four inch fletching (shield cut) is the fletching the same height and just angles down earlier, or is also slightly shorter?

Good day! On a min. width of quill, I just grind them to slightly wider than the feather base. I have heard of, and tried, to peel the feather away from the base of the quill, to have a semi-clear membrane with the feather attached. But never did have much luck. Two feathers of 4 inches or less is doable from a single primary. Never could get two 5 inchers. In my opinion, Secondary feathers are only good for flu-flu's or practice arrows...I always get too much flutter and a great deal of noise in flight. I am experimenting with shorter profile and shorter lengths. I only use 4" or less shield cut, 2-fletch. It adds about 4 fps chronographed going to 2-4" from 2-5". And by going from 3-5" to 3-4" added 4 fps.  2-fletch fits better in a quiver, more economical, quieter, faster...just tune your bow well, and you will find 2-fletch a real option.