The Problem Solvers Cable Doublers are made of light, durable machined and anodized aluminum and they are Teflon coated for a super-smooth cable pull every time. They come in two models. The first allows you to control two brakes with one lever. The second allows you to control one brake with two levers. Why? Well, there are myriad applications: tandems, cyclocross bikes, fixies, tricycles, recumbents, cycles for those with special needs, bike polo bicycles, those 4-person bikes you see on beach boulevards, and so on. You could even link both models of Cable Doublers together for the ultimate in redundancy!