What a neat invention this is!  Designed for prisoner escort officers both in the Police and Prison Service this natty wrist band is fastened to your wrist with velcro.  The bit next to your skin is soft leather but the bit that is in contact with the handcuffs is vinyl to allow the 'cuff to slide easily.  The really clever bit is the leather 'wall' each side which serves to prevent the handcuff sliding off.  The medium size inner circumference varies between 6 1/2  and 9 inches (165-227 mm)  This is an essential accessory to protect both the escort's and prisoner's tendons