I've had new bolts snap when fitting and had to use the old bolts again, the new bolts were just defective or low grade ,even though you shouldn't use second hand blade bolts in case they have stretched and are weaker ,normally it's not worth the risk of using second hand blade bolts , I've heard a few stories of people getting injured from second hand blade bolts letting go.
The Rover bolts are missing a 1/4 of the thread because of the flat side that locks into the blade plate so I wouldn't use a rattle gun on these types of bolts in my opinion it's best to use a ring spanner or socket set.
