Trucks come as a pair.

Size information: 

140mm - axle width 8.11" - for decks 7.75" to 8.125"

145mm - axle width 8.3" - for decks 8.25" to 8.5" 

150mm - axle width 8.5" - for decks 8.25" to 8.5" 

160mm - axle width 8.9" - for decks 8.75" to 9"