The filler flaps for sanding systems are manufactured in several versions. Their shape and equipment depend on the individual design according to customer requirements. They may be made of stainless steel, aluminium alloys, or general structural steel. The surface treatment may be done according to customer requirements. They may feature other accessories/equipment, such as sand level signalisation, or a door open/close sensor. The sand box may be refilled with sand using generally available external sand refilling systems. The filler flaps are lightweight and provide protection against unauthorized access.