This Smith-Victor UM5 Umbrella Mount with 1/4"-20 Top and Bottom
is used to mount a light and an umbrella onto a light stand or tripod. It allows the light to swivel back and forth 90°, and lock with a ratchet handle.
It has a 1/4"-20 in screw thread on top, with the same sized opening on the bottom.
Three things I like about this. It's small and light. It positions the umbrella shaft closer to the flash head. And, with one side uncluttered by knobs or handles, it's possible to position a hotshoe flash on a bracket so that it hangs down alongside the umbrella mount, putting the flash head right next to the umbrella shaft. This produces more even light on the subject. The only drawback I've found is that a reflector attached to a strobe head (e.g. Lumedyne) may obstruct the hole for the umbrella shaft. The solution is simply to raise the head a bit by putting a stud between it and the umbrella mount. I just noticed that B&H carries an identical product by Medalight at a lower price.
Wanted something small, light, fast, easy, no gimmicks, no parts to have to attach or that might fall off. It is all of that. Perfect. Under battlefield conditions it gets out of my way and simply holds an umbrella and an sb800 with easy adjustments. No muss. No fuss. It's durable enough. I suppose I might break one every 4 or 5 years -- or maybe not. That's ok. I'll buy more if needed. They're worth it.