https://www.modernmuzzleloader.com/threads/making-a-qrbp-from-a-5-8-x-15-x-2-bolt.34073/
Snidely70431 Member Joined Mar 10, 2018 Messages 420 Jul 16, 2019 #1 https://www.modernmuzzleloader.com/threads/making-a-qrbp-from-a-5-8-x-15-x-2-bolt.34073/
OP OP Snidely70431 Member Joined Mar 10, 2018 Messages 420 Jul 17, 2019 #2 That should be 5/8 x 18 bolt. 18 threads per inch.