They come in 2 sizes: for the 1/2" capacity Gibbs, the bolt measures 1 3/4" (not counting the head) x 3/8". For the 3/4" capacity Gibbs, the bolt measures 2" x 3/8" (again, not counting the head). Got to be grade 8 as well.
Its called a shoulder bolt. You can buy them from good hardware stores or bolt companies.
The nylock nuts are longer because of the nylon ring pressed into the top of them.
The bent thread nuts are a bit more streamlined. Bent thread nuts have the last thread pressed a bit so the nut threads are very tight and will not loosen.
Used on interior engine parts or applications where their is alot of heat. I use the bent thread nuts on my chipper blades, for example.
Grade 8 bolts are very hard and strong, but also are brittle. Grade 5 (plow bolts) are slightly softer so they distend before shattering or shearing.
A high strength all-metal lock nut that gets its locking feature from deformed top threads. Very reusable and good to 450 degrees F. Used on grade 8 cap screws and other high strength fasteners.
A socket head cap screw works nicely for Gibb's too. The head drops down inside the plastic plate on the side and sits on the shell of the ascender.
Has anyone had a spring pin from a Gibb's open accidentally? sometimes I wonder if this is a case of urban mythology. I sure can't argue with the idea of bolting when using it for a lanyard but I do wonder if the triple autolocking/unlocking of the spring pin isn't enough safety.