At SDJ Sports we appreciate that if you are new to cycling the sport can appear to be confusing with so many different styles of riding, racing, bicycles and not forgetting the all important riding accessories, clothing and equipment!
You would expect a cable is a fairly standard part of a bike. There are many to choose from though.
Gear cables vary in diameter and quality of steel. Stainless steel cables are used by many as they last longer and don't suffer with corrosion as badly as plain steel cables. Higher quality components use thinner cable so that the movement within the outer cable is smoother therefore offering a slicker gear shift. Shimano and SRAM make use of the same sizes usually but Campagnolo shifters only really accept Campagnolo cables as the end is a different shape and fit.
Brake cables are similar in so much that a stainless version is used by most for longevity and reliability. The end piece is different between road, hybrid and mountain bikes. Road bikes use a tear drop end to the cable whereas a mountain bike or hybrid uses a barrel shaped end. This is due to the compatibility with the levers used on each type of bike.