7 Inch Small used for Office desk height  ( gives a range of 440 - 520 mm ) 9 Inch Medium used for Production bench height ( gives a range of 460 - 580 mm ) 11 Inch Large used for Production bench height  ( gives a range of 520 - 700 mm ) 14 Inch Extra Large used for Architect bench height  ( gives a range of 620 -  860 mm )