Sits over the pop-up valve. This allows it to seal off correctly. Incorrect sealing can occur when abrasive is stored directly in the blast pot top bowl. Direct storage of abrasive occurs in auto-loading set-ups such as blastrooms and recovery systems. Pop-up valves do not seal well against abrasive. An incorrectly sealing pop-up allow air to escape. This accelerates wear and wastes compressed air. Adjustment of leg height allows fitting to different pots. Plate centers over valve by spider arms.