I made this one myself, you can get uni-strut at Lowe's
1-5/8" x 3/4" I think they are 12' long
I cut the main rail 6' long and the two shorter ones 16"
You need two washers out of 1/4" thick steel and two 3/8 allen head bolts, two more bolts for the pins (Poles) below (you can't get a wrench under there)!
My Poles (pins) are 1" round 2-1/2 tall, drill and tap 3/8" on the bottom and drill and ream for 3/8" cold roll pin or long dowel pins, total height is 4-1/2" tall. you need the room for serving.
From pin to pin needs to be center to the bolt in the middle.
Start out with all 3 uni-strut in a line, now all 4 pins are in a line, measure from outside pin to outside pin is your string length. You may have to file one of the slots in the uni-strut to get the length.
Wrap you starting point on the inside pin I use cloths pins to hold the string.
wrap around how ever many strands you want and back to the starting place with the cloths pin.
Now you want to turn the other end without the cloths pin to 90 degrees, use a speed square to get it square.
Wrap your serving , now turn the same end back in line (all 4 pins lined up) wrap serving to finish your loop.
now you can do the other end with the cloths pin