Front Seat Mounting Hardware is often replaced with options that are intended to make the job of removal and installation easier
The seat hardware had been replaced with a hex bolt and washers. This was supposedly to make it easier to get the seat off and on. It works OK except for the last two positions. The bolt head keeps the engaging pin from fully inserting into the hole. This allows the seat to slip back and forth between the last two positions.
In the lower picture you can see the correct front AN 24-8A clevis bolt. The back are AN24-9A clevis bolts.
correct hardware - AN 24-8A clevis bolt in the front