In this study, failure analysis of piston which belongs to primary standard pressure balance unit is investigated. The strength analyses of the piston were carried out analytically, considering the work-loading conditions. All the analyses were conducted in line with the fundamental strength theories using the finite element method. The material analyses were performed by EDX spectrometer, and fracture surfaces were investigated under scanning electron microscope. Findings revealed that the piston was designed appropriately and the material selection for compression loading was made correctly. Results also showed that fracture could have occurred under small bending, torsion or the combined bending/torsion loadings. Viewed together, although the piston manufactured from WC-Co was designed appropriately for compression loading, the fracture occurred due to external torsion loading.