This spacer is needed when a new mechanical fuel pump is fitted. When SU changed from the 700 series pump to the current design, it required the use of a different spacer between the pump and block. This is because the length of the pump arms was different and the distance to the cam lobe must be maintained. Thickness is approximately 0.520". Gaskets are included. Ref: AUB5040, 12G4520, GUG705603GM.