a impeller shaft assembly is disclosed for use in a refrigerant compressor , and more particularly in a commercial high - speed centrifugal impeller shaft configuration . the impeller shaft assembly 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 .