Some tips:
Always start your bolts and nuts by hand at least 1- 1/2 turns before putting any kind of wrench to it, ratchet or impact.
If you turn the fastener backward in its hole you will feel the start of the threads drop into alignment, then rotate forward a couple of turns to start the fastener. (It takes a little "feel", you'll figure it out)
Get a cheap set of calipers to size bolts, or a thread ID plate from Harbor Freight.
To fix the bolt you'll need a thread file,
DO NOT RUN A DIE DOWN OVER THE BOLT, it will 1) cut it slightly undersiz on the pitch diameter and 2) its a cold formed threaded bolt and you'll create stress risers in the thread root.