These foam pieces can be placed side by side under a direct mount humbucker, or split between the two halves of your precision bass pickup. They are placed under the pickup to provide the upwards force to allow the mounting screws to adjust the height of the pickup.
These have springs in the middle to ensure a sufficient, steady and even force is exerted on the pickup. They have adhesive on one side so that they can be stuck securely to the underside of the two halves of the pickup.
The foam has a spring in the centre which really does make it more firm. The foam was easy to install and a much better replacement for the stock foam in my Sire P8.