When choosing coils you generally use a 2″ longer bottom coil and the same size top coil as the travel of the shocks.
For a 10″ coilover choose a 12″ lower and 12″ upper coil.
For a 12″ coilover choose a 14″ lower and 12″ upper coil.
For a 13″ coilover choose a 16″ lower and 14″ upper coil.
For a 14″ coilover choose a 16″ lower and 14″ upper coil.
For a 16″ coilover choose a 18″ lower and 16″ upper coil.
*** We do NOT do return on springs, We do an exchange for the springs. $5.00 per spring upon inspection. Freight to us and back is customer responsibility ***