These are made of a steel core with copper wound onto it. When bass strings are very old the tone becomes deader. There are over two hundred strings in most pianos. Each string is under a tension of up to 100 kilos. This enormous force is kept in check by a very strong cast iron frame.
Some old pianos have a wooden frame.
This tends to move under the tension of the strings and the tuning is not stable in these. The bottom end of the string goes over a 'hitch pin' and the top end of the string goes through a hole in the tuning pin and is wound round three or four times. The piano is tuned by adjusting the tension on each string. This is done by winding the tuning pin tighter or looser. The terms overdamped and underdamped apply to upright pianos only.