These are grade 8 steel center pins. They have 5/16x24 threads, and come with the nut.
This center pin is 6" from the shoulder of the head to the end of the threads. It has 5" of threads, which will allow it to be cut down if needed. The head has a slot so it can be held with a large screwdriver while tightening.
5/16 center pin head has a diameter of .500 (1/2) and a length of .375 (3/8)
These pins are sold seperately.