These are typically used to connect garage door track brackets as shown in the one image. They have a 3/8" square lug on the head that locks into the track bracket so it will not turn when you tighten the nut.
Threads are standard 3/8"-16 Coarse
Material is Zinc Plated Steel
Description
Garage Door 3/8 x 3/4" Track Carriage Bolts, (Pack of 50)