Direct replacement pair of progressive fork springs suitable for Triumph unit twins 500cc and 650cc 1967 to 1970 that use the shuttle valve type front forks.
The progressive spring reduces brake dive and helps prevent bottoming out of the forks under extreme braking or sudden bumps. The spring is rated for solo use , not for sidecar use.
NB, Please note that BSA/Triumph used different spring lower cups , check this spring will fit, it has dimension of 49.0mm OD & 39.5mm ID, if you have springs size of 51.5mm OD and ID 3.5mm , then see BSA part number SRM-97.1892-PRO
For fitment-tight coils towards lower spring cup.