Folks who've spent any time around a machine shop may have noticed that the collets holding drill bits or end mills to the mills and lathes are simple tapered shafts, without keyways or splines. They sit in mating tapers and require very little axial insertion or removal force- the friction around the surface transmits quite a bit of torque. The Morse Taper, invented by the inventor of the twist drill, is a very simple and very effective mechanism.
The folks at USE have been on a quest of late, it seems, to remove seatposts' fastening hardware from the forces that a saddle clamp sees. Why? We've all been on rides in which someone comes down hard on the saddle and it's hardware simply explodes. Some bigger riders we know even carry spare saddle hardware for just this reason. The Alien saddle head was their first in this direction. With it's two (and later one) very tiny M2 bolts holding everything together, it scared the bejesus out of a lot of folks, despite being plenty strong and very light.
Because of my Maverick Durance's laid-back seat tube (not to be confused with seat angle- it's offset from the BB), and a chronically creaky Thomson post, I began to look for an infinitely adjustable, lightweight and strong post. (The Maverick requires the Thomson to be at the very edge of it's adjustment range, and certain saddles would be pointed slightly upward, in a numbing sort of way.) Again, Charlie came to the rescue with the USE Sumo. The lightweight (40g less than a Thomson Elite) Sumo uses two tapered caps that have grooves for the saddle rails and mate to the post head and a pair of clamps that tie the whole thing together (image, right, from Singletrackworld).
At the time of ordering, I was told by the local shop that Ibex Sports (the US distributor) couldn't get the 30.9 diameter I needed in aluminum, so carbon it is. It's a deceptively simple post. While the large diameter probably counters some of carbon fiber's damping effect, it sure looks sexy and is around 50g lighter than the Al version. The tapers bear the brunt of forces from the saddle and after a second tightening, it hasn't moved or made a peep in eight months' riding. The bolt proved to be about 3mm too long, so a few minutes with a Dremel cutoff wheel and de-burrer fixed that, and my thighs are much happier. If your saddle isn't pushed back on the rails (see image, right), this probably won't be an issue, though. Not cheap at $150 (approximately), but the aluminum version should run less. A small price to pay, though, to keep my todger happy. Altogether, a very clever and well-executed clamp that offers good reliability and excellent adjustability.