All Mountain Bike Parts Descriptions

#22) Seat Post - The post to attach your seat to your frame.   Seat posts come in so many diameters and lengths that I would say that there is no standard size. The old steel posts were a basic straight tube that tapered to a 7/8" or 22.2 mm size to accept a clamp built onto the seat rails.  The most common style now, has a clamp built onto the top of the post to attach to the seats rails. They come in many different materials for weight shaving and shock absorption, and they are priced shock absorbingly different as well.

Bike Parts Diagram