Actually...........guys............I'm not sure...........but...........I...........think..........I..........did...........this.........exact thing, WHY?
BECAUSE OUR STUPID LOCAL "fastenall" joint DOES NOT STOCK ANY 9/16 bolts!!!!!
I had a "like new" idler that had the wrong or no bolt, I do not remember. I used a mechanical locking nut. I believe the originals are supposed to have a castellated nut/ cotter pin