I'm trying to make a gate structure for my attic to prevent people from falling through the pull-down stairs opening. For this, I'm joining threaded iron piping together with elbow joints and t-joints. The problem is that when I try to make a rectangle with four sections of pipe and four elbows/t-joints, I can't attach the fourth corner together because tightening the fourth section of pipe into the fourth joint by turning it clockwise would un-screw the third joint because it would be turning counter-clockwise.
Here is a photo of what I'm doing:
I feel like I'm missing something obvious. And when I googled it, I found this site for building shelves with similar materials and a similar method, but it doesn't mention the problem I'm having.
Could someone please help?