A block with lead or another relatively soft material on its bottom. It is made up on drill pipe or tubing at the surface, run into a well, and set down on the object that has been lost in the well. The block is retrieved and the impression is examined. The impression is a mirror image of the top of the fish; it also indicates the fish’s position in the hole, for example, whether it is centred or off to one side. From this information, the correct fishing tool may be selected.