The Primary Series special alloy metal sound plates are 35 x 5 mm ( Soprano/ Tenor Alto) or 35 x 10 mm (Large Bass) in size. Each sound plate is printed with the note image of the corresponding note, which aids in learning to read music through visual reference.The resonance boxes of the Sonor Primary Matallophones are completely FSC® certified. Added to this is the use of an eco-logical lacquer system called Proterra, which is based on shellac, oil and carnauba wax.