What does it mean?
Prior art, also known as the state of the art, means that something is not (any longer) protected by a property right. It can be freely used commercially by anyone for any purpose without any restrictions or conditions.
A good example is a piece of string used to tie an ordinary knot. However. For example, you may have a string made of a new material. This material may be proprietary and not prior art. So your string is probably protected. You have to check on a case-by-case basis. Rule of thumb: choose the “boring”, regular solution that has been around for decades and you should be on the safe side.
from sheep wool: prior art.
from wool but also with a wire inside to conduct electrical signals in wearables: might be protected.
a regular M4 bolt is prior art.
A M4 bolt though from a material that explodes for example or has an RFID chip build in might be protected.
So also with prior art. Look twice. Who made this part. And is something added that might be protectable and be protected. Go for the simplest, easiest oldest solution. And you’ll be sure.