Hi Jonathan, I am referring to this part below when installing the diff into chassis. 13 Remove the upper mounting bolt (1) and refit with washer (9) under the bolt head. Centalise the differential using washers (16) and (12), as required, between the metallastic bushes and the differential. Use a further washer (9) and nyloc nut (6) on the end of the bolt. Tighten the upper mounting bolt and lower mounting bolts to 40 lbft (55 Nm). Check that the differential is central ± 2mm. Adjust if necessary. The chamfered washer is (9). They wasn't fitted on my car originally and just look like they will clamp the inner and outer metal part of the bush when tightened up.