A correlation developed by Holm for thermal contact conductance measurements made in vacuo is discussed and its physical basis is deduced with the help of dimensional analysis. On modifying Holm’s treatment by including surface roughness and neglecting nominal contact area, the analysis yields a dimensionless conductance C* = C/σk and a dimensionless load W* = W/σ2M. When 350 data points from the literature for aluminum and stainless steel contacts in vacuo are plotted in this form C* is found to be proportional to about W*0.73 with correlation coefficients of better than 0.9. The correlations for the two materials do not coincide, however, and this and other discrepancies are discussed.

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