When I think of carbon fiber, I think of its automotive applications, like F1 guys making monocoques out of the stuff. But it never occurred to me that carbon fiber could be used to make the hand tools we use to work on cars. A company called CarbonLite Tools is now producing a line of carbon fiber box-end wrenches.
The wrenches are, of course, insanely light; a set of five weighs just 6.7 ounces (190 grams), which the company reckons is lighter than your average steel single 15mm wrench. And yet they're not made completely from carbon fiber—the teeth are made from hardened stainless steel inserts, which you can see in the photo below, so that stubborn nuts won't shred those expensive layers of fiber.
And yes, they are expensive: A set of five—metric on one side, Imperial on the other, from 3/8" & 10mm up to 5/8" & 15mm—will set you back US $140. Beyond the price, the only thing that might give you pause is this caveat from the company: "We recommend using gloves as there is a small possibility the carbon fiber can leave splinters in your hand if the carbon fiber is damaged. The possibility of splinters from the carbon fiber wrench is about the same as with a wood handle on a shovel or hammer."