Large, circular boss-grip shields were the standard in much of Europe throughout the Viking Age, and shields with a boss have been used by various cultures around the world from antiquity well into the middle ages.

This 2mm steel shield boss was created by Matthew Finchen, a UK based Armour-smith of Lancaster Armoury, maker of bespoke high end arms & armour, as well as munitions grade & buhurt. 

Approximate specifications are as follows: 

Weight: 776g
Total Diameter: 22.5cm
Inner Diameter: 15cm
Depth at centre: 6cm
Material: 2mm High-Carbon Steel