First off, let me say that this is far from my idea. I think it originally came from Mr. Strobist himself, though I have seen several other versions online lately. Secondly, this is not on the same level as a SuperClamp and it is not intended to replace it in your bag. This clamp can, however, be a very inexpensive and versatile tool for mounting light weight gear to many objects.
Here is a basic 2" A clamp. This particular model can be purchased at Home Depot for $o.99. Right now you should run down there and buy a dozen or so of these, they are incredibly useful and a rare bargain in the photo game. For some reason the store brand clamps with the green tips only cost a dollar while the Pony brand clamps of equal size (sitting right next to them) cost $2.99. The Pony clamps are also sold in the grip departments of many photo supply houses and are a standard in the woodworker's shop as well. To be honest, if you look at the two side by side, you will notice that the Pony brand clamp is made of slightly heavier gauge metal and the rubber tips are just a bit thicker as well. I don't think that these small improvements are worth paying triple the price per clamp, but if you think they are, then by all means get the deluxe clamps.
If you notice in the picture above, I have removed the rubber from the "handle" portions of the clamp. When you do this, you will expose a 1/4" hole on each side of the clamp. The next thing that you should do is drill out those holes to 3/8". You may want to file off the back side of the hole if there is a bur left when you are done. The reason for this is that a wing nut is going to be tightened against that surface later on and any rough edge may act like a lock washer and make loosening the nut difficult. Oh yeah, DON'T USE LOCK WASHERS! Actually, you can if you want, just don't expect to be able to remove the wing nut by hand (isn't that the point of a wing nut?). You should not need a lock washer anyway. You can get the bolts plenty tight by hand and if you are using this clamp in an environment that warrants the sort of security that a lock washer provides, then the point of failure will probably be the clamp slipping, not the wing nut becoming loose.
The reason for drilling out the holes is that they will now accept our home built 5/8" studs. If you are going to use a commercially available stud for this project then you can skip the drilling step because most of these studs can be attached via a 1/4" bolt and the stock hole. The next thing that I did was rig up some of the old umbrella swivels that I had to fit the clamps. These swivels were from when I was just starting out in the OCL game and they never worked very well on a light stand. They are the ball-type cheapy swivels that can be found on ebay. It was a bear to adjust them with an umbrella attached and they could not be tightened enough to prevent slipping when it was windy. You can still find the particular model that I have on ebay for about $8 and they work pretty well with these clamps. If you do decide to purchase some, keep in mind that there are two kinds: ones with a 5/8" stud socket and ones with a 3/8" threaded hole. I am using that latter, but the choice is up to you. If you plan on giving them dual duty on the clamps and light stands, I would get the one with the 5/8" socket. If you are just using them on the clamps, get the 3/8" threaded kind.
In an ideal world I would have used a plastic knob with a 3/8" bolt to attach the swivel to the clamp. As it happened, the local hardware store was fresh out of the size that I needed; so I made my own out of a bolt, a wing nut, and a nylon lock nut. You can see how I put it together in the photo. This option was about the same price as a knob, so I didn't save any money on it, I was just working with what I had at the time. If you plan on making these in bulk I would recommend ordering knobs in bulk online or things could get pricey real quick. By the way, the washer looking thing in the photo is a chrome 1/8" thick spacer that I had laying around. DO NOT BUY THESE! they are like $3 a piece and a couple of regular flat washers ($0.06 total?) will work just as well. I was just using what I had.
So here is what we have so far: A DIY 5/8" stud, a modified $0.99 A clamp, and a light duty umbrella swivel with a home made knob. Now, here is the tricky part. You must un-thread the wing nuts from the stud and the swivel, stick the 3/8" bolts through the 3/8" holes on the clamp, then replace the wing nuts and tighten. Got it? Oh, never mind that was easy! Now make a few more and go take some cool photographs. Just in case you got lost on that last step here is a picture of what it should look like.
Now you have a clamp that you can use to mount a speedlight to a variety of objects (or two speedlights if you add another swivel to the 5/8" stud). It can also be mounted to a light stand via the stud to act as a clamp or a swivel (or both at once). I made 10 clamps for myself and the total cost was less than $25, not including the umbrella swivels which I already had. Only two of the clamps that I made have both the swivel and the stud, the rest only have the stud. Even if you have to purchase the umbrella swivels the total cost should be under $10 per clamp. I hope you found this useful, next week we will be building a "double stud adapter". I just made the name up but I think they are pretty useful, hopefully you will too.