I occasionally use 1-1/2 in. dia. steel pipe for handrails. It is plenty sturdy and easy to grip. But it needs something other than a 1-1/2 in. dia. cap threaded on its ends to look presentable. As shown in the drawing, I use a 1-in. dia. cap threaded onto a 1-in. dia. nipple instead. I wrap the nipple with a couple of turns of electrical tape to ensure a tight fit. The nipple is held in place by a 3/16-in. dia. stove bolt that is run into a hole drilled and tapped into the pipe and nipple from below.
Walter D. Cotton, Wellsboro, PA