Qty 2 - 2x4 8 foot long
Qty 4 - 2-1/2" Hex head 1/4" Bolt, 1/4-20 thread
Qty 4 - 1/4-20 Nylock Hex nut
Qty 12 - 1/4" ID, 1" OD fender washers
Qty 32 - #8x1-1/2" Deck Screws (Do NOT use drywall screws - they are brittle and will snap!)
6' of 1/8" Nylon Line
And here are the drawings (Click to enlarge - you should be able to save and print these JPEG format files) :
To start, I ripped one of the 2x4's into three 1" wide by 1-1/2" tall strips - reserve the scrap for later as it will have a use. Cut the pieces to length and add the 20° cuts to the ends. I found a miter saw to be very handy for this. I then cut a 24" long piece of the second 2x4 and ripped it to get the top pieces. I then cut the pieces I didn't get out of the first 2x4 out of the remainder of the second one. There should be enough left to cut a piece that is cut down the middle of the 2x4 at a 20° angle to use as French cleats to be able to hang the sawhorses on the wall if you so desire.
To drill the holes, I used a drill press to assure myself that the holes would be square. I also made sure that I measured all of the pieces from the bottom to be sure that the hinges would be properly located.
To assemble the inner leg assembly, I took the piece of leftover scrap from ripping the first 2x4 and cut two sections 18" long. These were put on the bench and the 20" stretchers were put on top of them. The scrap acts as a spacer to roughly center the short stretchers on the inner legs. I pre-drilled the holes for the screws in the inner legs and then put glue between the stretchers and the side rails. Clamping the pieces in place, I then screwed the parts in place using the deck screws. (two per joint)
The outer leg assembly is a bit trickier. The long stretcher is put on the outer legs, pre-drilled, then glued and screwed in place. Be sure the legs are square to the stretchers and that the legs are parallel. Similarly, pre-drill, glue and screw the top to the ends of the outer legs.
Now that the two leg assemblies are complete, insert the bolts through the appropriate holes from the outside. There shoudl be a washer underneath the bolt's head, between the inner and outer leg, and on the inside of the inner leg before the nut is installed. It will be difficult to get the washer between the inner and outer legs, but this is necessary. Tighten to get an appropriate amount of friction.
Cut the nylon line into two pieces and seal the ends with a flame. Tie a loop around each of the bottom stretchers to keep the legs from spreading too far.