This is the rear shackle pin for the SWB Silver Wraith models prior to H Series.
All Bentley R Type, Silver Wraith and big boot Silver Dawn models had a 2.25 inch wide rear spring which required similar length shackle pins and bushes.
The original bush for the Silver Wraith models was FW1938 which is NLA but the R Type bush RF7636 is a suitable substitute - the only difference is that the oil feed hole on the R Type bush is 0.500" and on the FW1938 it was 0.300".

Silver Wraith from A to G Series