Trucks come as a pair. 

Size information: 

109 - 6.9" axle - for decks 6.25" - 7.6"

129 - 7.6" axle - for decks 7.4" - 7.8" 

139 - 8" axle - for decks 7.8" - 8.2" 

144 - 8.25" axle - for decks 8.2" - 8.375"

149 - 8.5" axle - for decks 8.375" - 8.6"

159 - 8.75" axle - for decks 8.6" - 9" 

169 - 9.125" axle - for decks 9" - 9.5"

215 - 10" axle - for decks 9.5" - 10.5"