[rohrmann]

They are the pivot pins connecting the springs to the frame via pieces of metal called shackles. Instead of plastic bushings with just a plain bolt, 'wet bolts' refer to bronze or brass bushings with bolts that have a hole drilled part way through from one end and then have another hole cross drilled about centered where the center of the spring would be, then a zerk fitting is installed enabling grease to be applied to lubricate the bolt to bushing surfaces. This makes for a very durable system as long as grease is applied on a regular basis.