I have bolt knobs for sale. THey are threaded for 5/16 - 24 TPI. They come in flat black Moly Resin finish by John Norrel.
If interested here is the link you can purchase them.
http://www.bigrivertactical.com/catalog/item/2195032/5933264.htm
If interested here is the link you can purchase them.
http://www.bigrivertactical.com/catalog/item/2195032/5933264.htm