FSA's aluminum KFX crank arms are machined in two separate pieces before being glued together.
If you want lightweight and high-end components, and especially cranks, the usual answer is carbon fiber. But FSA, who have plenty of fancy carbon things in their catalog, is going a different route with their upcoming aluminum KFX arms.
There are countless alloy cranks out there, though, so what's so interesting about these? Instead of machining them from a single piece of aluminum as per usual, they're made in two halves before being glued together. Yes, they're glued.
See those ridges and channels? They slot together very precisely to create a single unit.
Now, if know Cannondale well, that process might sound a bit familiar; they do a similar thing to make their impressive Hollowgram Si arms. The idea is that by machining them in two halves, FSA can remove as much material from the inner face of each arm as possible, making for a hollowed-out structure that's said be relatively lightweight yet strong enough for downhill and enduro use.
One arm is left with very precise channels cut into the mating face, while the opposite arm gets thin ridges that slot into said channels and, with the help of some powerful glue, make for a single crank arm.
Machining the arms in two pieces lets FSA remove material from inside that they otherwise wouldn't be able to reach.
I was told that they'll weigh in at around 520-grams (arms and spindle) so while they're certainly in the svelte category, they aren't the lightest around, either. FSA doesn't have any plans to move away from carbon fiber, they told me, only that they wanted a solution that's relatively lightweight but without the sometimes fragile nature of carbon. There's no word on an MSRP yet, but you should see them on shelves by late-summer.