"Spangenhelm" is a Germanic term often used to refer to helmets constructed with metal bands (spangen). This type of helmet was used in Europe from the Late Antiquity to the Middle Ages.
This specific example could be framed between the 8th to 13th centuries, being probably its most common use between the 9th-10th centuries. It is easy to find manuscripts showing warriors wearing this kind of helmet until the 13th century.
It is made of 1.6mm steel, reinforced with 1.6mm riveted bands and a 3mm thick nasal protection. It has an interior suspension system with a slightly padded fabric, riveted to the inner perimeter of the helmet. It also has a leather strap with a brass buckle.
M: The inner circumference measures 61 cm, forming an oval of approximately 18 x 21.5 cm.
L: The inner circumference measures 64 cm, forming an oval of approximately 19.5 x 23.5 cm.