Note: If you need this to work with any different diameters of crossbars or want to use a diferent screw thread insert, drop me a note and I'll change my design accordingly.
I have one of those cheap photography backdrop sets consisting of light stands and three crossbars which you can connect and attach a backdrop to. Thing is, each of those crossbars is ~1m long and the way it's designed you can only use the set with all three crossbars at once, or not at all which is obviously stupid, especially in situations where space is limited.
So I figured out a way to modify this set to make it possible to use with 1, 2 or all 3 crossbars. It's pretty easy to do, too.
The original set comes with this configuration:
2x Light Stand Attachment + Female End
1x Male End (with spring clips) + Male End (with spring clips)
What you need to do is drill out the rivets of one of those male ends and attach it to one of the sections with a Light Stand Attachment, converting their female end into a male end. You can rivet it in place or if use a screw with a nut if you don't have a rivet gun.
At this point you have:
1x Light Stand Attachment + Female End
1x Light Stand Attachment + Male End (with spring clips)
1x Male End (with spring clips) + Female End
This allows you to use either 2 or 3 crossbars. What you're missing to be able to use just one crossbar is a light stand attachment adapter which clips over the male end and allows attachment to the light stands.
And that's exactly the part that I have designed here, which works great with my backdrop set!
It is obviously designed to work with my setup (see sketch for the dimensions), but if you need alterations I can do that easily. If your setup is identical you'll be needing an M5x10x7 threaded brass insert and an M5 thumbscrew to make it work properly / securely attach it to light stands.
After printing you might need to to some filing and / or drilling for cleanup.