Whats better to use
 

My upper control arm ball joint nut went bad.... Nylon type lock nut M10 1.25 17mm...No threads left, so I went to napa & O'Reillys, all I could find was M10 1.25 in a 14mm grade 10 & at the hardware store I found a Nylon type M10 1.25 17mm but unknown grade... what one do I trust... the thinner wall 14mm grade 10 with no nylon, or the 17mm unknown grade but appears to match original? Any one with simmilar experience & have some advice, Thanks!

Looks like the nylon one from the hardware store has a |8| on the back.