Fastening member

A fastening member (100) for fastening a first component (118) to a second component (110) in an end-to-end configuration along a common axis (A) is disclosed. The fastening member (100) comprises a first portion (124) having a threaded region for engagement with a corresponding threaded region (120) of the first component (118), a second portion (126) for applying a retaining force to the second component (110) to hold the first and second components (118, 110) in sealing engagement, and a deformable portion (130) intermediate the first and second portions (124, 126). The fastening member is particularly suitable for use as a cap nut in a fuel injector of the type having a cylinder pressure sensor integrated into the cap nut.