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This purpose of this paper is to examine the relationship between crack growth equations based on Elber’s original plastic wake induced crack closure concept and the fatigue threshold as defined by the American Society for Testing and Materials (ASTM) fatigue test standard ASTM E647-15el. It is shown that, for a number of conventionally manufactured metals, the function U(<i>R</i>), where <i>R</i> is the ratio of the minimum to maximum applied remote stress, that is used to relate the stress intensity factor Δ<i>K</i> to the effective stress intensity factor Δ<i>K_eff</i> is inversely proportional to the fatigue threshold Δ<i>K_th</i>(<i>R</i>). This finding also results in a simple closed form equation that relates the crack opening stress intensity factor <i>K</i>_o(<i>R</i>) to Δ<i>K</i>, <i>K_max</i>, and the fatigue threshold terms Δ<i>K_th</i>(<i>R</i>) and Δ<i>K_eff,th</i>. It is also shown that plotting <i>da</i>/<i>dN</i> as function of Δ<i>K</i>/Δ<i>K_th</i>(<i>R</i>) would appear to have the potential to help to identify the key fracture mechanics parameters that characterise the effect of test temperature on crack growth. As such, for conventionally manufactured metals, plotting <i>da</i>/<i>dN</i> as function of Δ<i>K</i>/Δ<i>K_th</i>(<i>R</i>) would appear to be a useful addition to the tools available to assess the fracture mechanics parameters affecting crack growth.