Surly Constrictor Seat Post Clamp
The Constrictor was designed specifically to end slipping seat posts. The extra-thick clamp utilizes an 8mm stainless bolt and accommodates a rear cantilever brake hanger, if you decide to go that route. The Constrictor is machined out of aluminum billet and black anodized. It's available in 31.8mm, 33mm inner diameter sizes.