A threshold is installed at the base of the frame of the door. In some cases it also acts as the base for the door frame itself. It is located just outside the door and acts as a seal for the small gap that is left between the door and the floor. A threshold is principally made out of 3 prominent materials:
Wood: This threshold is very simple to make because all you will need is a thick log or panel of wood, that fits into the length of the door. You will need a saw to cut and shape the wood, and nails and a hammer to fix the log into the door space. If you are planning to make the threshold as a do-it-yourself project then a chisel and hammer will make excellent tools to make simple yet fascinating designs on the wood.
Concrete or Stone: The ones that are made from stone are more expensive and you will need a lot of efforts to install the stone one, as it needs cutting as per measurements, toning, and finishing. Installation of such a threshold requires concrete in small amounts and appropriate niches in the door frame itself are made in some cases. It goes without saying that these threshold are expensive to install.
Metal or Polymers: Of late, several companies and manufacturers have started manufacturing smaller, much well designed and kind-of-compact thresholds. They can be simply glued down on to the floor and then can be enforced or further affixed on the floor by a drill and then a screw. They are the best for air-conditioned or carpeted homes, as they almost seal the door frame air tight.