“Yes!” I thought as I reached the jug after the crux on Center Route. I had a .5 cam 10 feet below my shoes I knew was bomber – it nicely held the 15 footer that followed my graceful ejection from the crux. However, now I needed another piece or I would be risking a 25+ foot fall. I had brought a rack of singles and was staring at another perfect .5 placement. My .4 was also sitting snugly below. I tried to squeeze in a .75, but it was too big. My feet, on nothing but featureless sandstone, began to tighten as I alternated my hands between a burly finger lock by my waist and the jug that was feeling more and more like a mediocre sloper. The pump factor increased as I rattled around the .3 only to confirm that it was too small. The burning in my arms was getting more severe by the second as I actively thought that I didn’t have time to find a decent stopper placement. I needed a cam, stat. One more quick shakeout and I threw in a #1 C3 in the narrow taper of the seam above. I tossed the rope in, yelled “Take!” and rested. No problem.
A year ago I ponied up for the 2, 1 and 0 Black Diamond C3 cams, thinking I would use them primarily in specialty situations. Since then, they’ve become vital tools in my protection arsenal. Along with Center Route, the C3s have been essential on many Eldo classics including, Rincon, Five-Ten Crack, Climb of the Century, Aerial Book, Over the Hill, P1 of Genesis and others. I’ve always said that it takes big nuts to climb with small nuts, but the C3s substitute nicely when in a jam and in need of a quick placement. Eldo is known for its scary, tough climbs with bolts and Pitons concentrated only enough to keep you off the deck. The 5.11s there are a different world and in such a place, the C3s can be a huge part of making the climbing accessible.
The C3 cam head is significantly shorter in length than the traditional C4 design, an advantage magnified by the reality that very narrow cracks tend to be quite non-uniform. This makes the C3s superior to other brands that employ four lobes and to designs that bracket the lobes with parallel stems that run the length of the cam head.
Unlike Aliens, the C3s have stiffer stems with a strong dual spring-loaded trigger. This is an essential attribute that helps with “fishing” for a placement, a common occurrence on thin cracks.
If you are looking to establish a rack of doubles or more, note that the #2 C3 is the same width as the .3 C4. Also worth note is that the 000 C3 is only rated for 4 kN. The C3s run at $70 apiece, but if you’re a total scum-bag climber, keeping your eyes open for deals can often lessen the pain. 
The .3 C4 and the #2 C3 have the same width but one can see the C3 has a much shorter head.
For my birthday, my roommates came up huge and got me the 00 and 000 to complete the set. I can’t wait to get outside when the weather permits to test them with some huge whippers!
These are an ESSENTIAL part of my rack. When I don't know what to take on a route, I take these. They're light, easy to place, and seem to fit everywhere. My only beef is that they don't have the hemispherical range of an Alien, but just keep that in mind when you place them.