Taken me awhile to put this together, but it seems alot of people don't have access to a chin up bar. So here is a really easy and cheap way to make a bar that you can attach to things like football up rights or even rafters, doesn't matter if its a round tube or a square.
Supplies:
1" Bar, you can use thicker, or things like old moutain bike handlebars, any tube basically.
Length of rope, give or take double the length of the tube plus about 2 feet.
Cable clamps, not needed but will make it alot safer
For those of you that don't know what cable clamps are, they are just like exhaust clamps but really small, they are designed for aircraft cable, so crank them on and they will not slip. If you don't want to buy them use a tight knot and tape around it so the knot can't come loose.
Now simple enough slide the rope through the tube and again you'll want about twice as much length and about 2 feet or more, the more aditional rope you use the easier it is to mount and take off, but the more swing you'll have. Then clamp the ends together using the clamps
Now your all done and just have to use it. Incase you can't figure this really simple process out, place the rope on one side of the object and the pole on the other side, now slip the ends of the pole on the inside of the loop of rope, pull tight and it will not let go and should basically center it's self. Here is an example on two 2x4's in my garage.
Cheers.