This gorgeous (in a rough sort of way) bit of magnesium casting is an insert designed to go inside the tire of a military HMMWV (pronounced Humvee) to keep the vehicle moving even if the tire blows out. I assume it's made of magnesium because when wheels are spinning very fast, every bit of extra weight increases the gyroscopic effect when you attempt to turn the wheels. Magnesium is quite commonly used in race cars and high-end sports cars because of its light weight.
The fact that it's also flammable would seem like a disadvantage particularly in a war zone, but actually solid magnesium is surprisingly hard to light. (I have a story about the relative flammability of different forms of magnesium.)
This stuff is definitely real, fairly pure magnesium. I have a third half-wheel that came with the set in the photograph, and a small chip broken off that one lit and burned exactly like real magnesium. Amusingly these were actually offered on eBay as camp fire starters: Any block of magnesium can be used that way by scraping off some curls of metal with a hunting knife, then lighting them with a flint. But eBay canceled the listing for violation of some policy or other (not sure which one, since camp fire starters are routinely sold on eBay, as well as at Walmarts all over the country).
I don't even want to know what the military originally paid for these things, but I think $10 per half-wheel is a pretty fair price for such a lovely bit of magnesium.
Contributor: Theodore Gray
Acquired: 26 June, 2006
Text Updated: 29 January, 2009