Aircraft make, model and serial number are not sufficient to ensure the correct replacement spring as many aircraft may have been originally equipped with either one or retrofitted with a conversion kit. If the spring you are replacing is marked with a brand name (e.g. P.L. Porter or Stabilus) the correct replacement is readily identified. The coil spring/hydraulic style are also identifiable by a 1ΒΌ" diameter visible coil spring. The thread may also be measured to verify the correct identification.