Set of skateboard trucks. You choose your trucks based in the size deck you ride. Decks under 7.5" ride 107-120mm (4.25-4.75") trucks. 7.5" decks use 120-127mm (4.75" or 5.0") trucks. 7.6-7.9" decks use 127-129mm (5.0" trucks). 8.0-8.25" decks use either 129mm (5.0") or more common 139mm Trucks (5.25") trucks. Over 8.5", Longboard or Oldschool decks use 149-169mm (6" or 7" trucks).