The HANDLEBAR ADAPTERS are made of ALUMINUM, have a specific attachment to make it possible to mount our items to the ORIGINAL HANDLEBAR, for example: Pro-tect lever, Bar End mirrors and Antivibration. They are sold in pairs and are specific to individual motorcycle brands: Yamaha, Honda, BMW, Kawasaki, Triumph and Suzuki. THE ADAPTER cod. NB1016 is instead a UNIVERSAL expansion attack and is used to mount our articles on handlebars with internal diameter 13 or 17 mm: Lever Pro-tect, Bar End mirrors and Antivibration. THE ADAPTER cod. NB1016 is sold individually. THE ADAPTER cod. NB1016-13 is UNIVERSAL with expansion and is used on handlebars with internal diameter from 14mm to 15mm. THE ADAPTER cod. NB1016-16 is UNIVERSAL with expansion and is used on handlebars with internal diameter from 17mm to 18mm THE ADAPTERS cod. N1016-13 and NB1016-16 are sold in pairs