[SEL] OT Strange bolt.

[BillMil357 at aol.com]

Hey Men, I was mounting a seat on a 1972 Cub Cadet Lawn tractor that I am  
restoring and a fellow gave me four 5/16 in. bolts to mount it , three of the  
bolts were fine but the other one I could not get the nut started, checked  
closer and I could not see a taper of the threads on the end for a left hand or  
right hand thread, I took one of the other bolts and put my thumb nail in the  
second thread from the end and turned the bolt to the right and my nail moved 
 right up toward the head of the bolt, I did the same thing to the other bolt 
and  my nail never move, it stayed in the same place on the bolt, turning it 
to the  right of the left, so this bolt just had grooves cut into it straight  
around the bolt and not connected to the next groove, has anyone ever seen 
one  if so what in the world are they for, it would mesh right in one of the 
other  bolts same amount of grooves per inch. In my 76 years on this earth I have 
never  seen anything like it, someone give me some info. on this it bugs me 
Ha Ha. I  bet you people thought I was gone but I browse on here every day.
Thanks,  
Bill Miller.
Memphis, TN.