includes a contoured spacer body the contoured spacer body includes a front face a rear face a recessed spring bearing surface in its rear face and a spring spacing abutment including a shoulder that is seated against a protective washer the contoured spacer body functions to prevent the headed front end of a fastener from coming into direct contact with a spring assembly and protective washer consequently the spring assembly and protective washer are not sized to correspond to the cross section area of the headed front end as disclosed in the prior art instead the protective washer and spring assembly are sized to fit the rear face of the contoured spacer body which in turn is sized to fit the front face of a first stage impeller the contoured spacer body ensures that the clamp load is dissipated across the front face of the first stage impeller the contoured spacer body also provides greater protection to the first stage impeller during installation and maintenance in another embodiment the contoured spacer body and headed front head are combined to make a contoured front end application_number US 92872501 A description while the invention will be described in connection with one or more embodiments it will be understood that the invention is not limited to those embodiments on the contrary the invention includes all alternatives modifications and equivalents as may be included within the spirit and scope of the appended claims 0038 fig1 schematically shows a mechanical chiller 10 including a compressor 12 a heat exchanger such as a condenser 14 an expansion device such as an expansion valve 16 and a heat exchanger.