Small, lightweight and versatile - what's there to think about, just get one or two of them. The 'tube' seems to be aluminum, but the little 1/4" - 1/4" plug and the 1/4" - 3/8" inlay screw is made of another and heavier metal.
Full name: 1/4" 3/8" 5/8" Spigot Adapter Screw for Camera / Flash Trigger / Mount / Light Stand / Tripod
Webshop: DX.com (Deal Extreme)
Price: $3.50 (Free shipping)
This little versatile 'thingy' is just one those things you need in your tool box. When you suddenly need it and don't have it, my guess is you'll be cursing and regretting not putting in an order for it.
None I can think of as of now.
Buy it here