I believe its called a ‘Polycolum’. They are sold in(if memory serves) in 7’&8′ lengths in diameters of 3.5″ and 4″ at Home Depot,Lowes,etc. They are concrete filled metal pipe. A buddy of mine had a bunch cut for a project. Unfortunately, they were all cut too short. Gave me one to play with. It is just under 5′ long @ 59 3/8″ and weighs 61 lbs.
My favorite 3.5″ Bar exercise is Walking Overhead Tricep Extensions. Start with the hands at the end of the column, one hand below the other. At the top of each rep, move the top hand to below the bottom hand. Do another extension and at the top,again move top hand to below the bottom. Keep ‘walking’ the hands and see how far you can get down the column. Though the bar weighs the same, each rep as you move your hand down, gets harder. The column gets moved up and becomes harder to control. With each rep, you have more mass above the hands. It becomes quite hard to control. For some REAL FUN, once you’ve bottomed out, walk your hands back up in the reverse order.