In the 2007 ASME PVP conference, a presentation was given on the testing and subsequent fatigue initiation analysis of 304 Stainless Steel (304SS) instrumentation spacer rings that had cracked while installed in a thermal fatigue test loop . The instrumentation spacers contain ports radially machined through-wall for monitoring temperature and pressure. Routine flow-surface inspections revealed actively growing cracks emanating from each port. In this work, three dimensional finite element models (FEM) were constructed from the available test measurements and used to obtain, via elastic Finite Element Analysis (FEA), representative stress histories for each machined port of the spacer ring. The FEA stress results were used to perform fatigue usage and crack growth curves using 304SS material models adjusted for low-oxygen water environments to determine the fatigue initiation and crack growth characteristics of the spacer ring cracks. Destructive examination and metallographic results of the spacer rings are compared to the analytical fatigue initiation and crack growth results.