A fastener including: a first load receiving portion and a second load receiving portion ; a strainable portion between the first and second load receiving portions; a measuring end including an alignment protrusion ; a cavity extending from the measuring end of the fastener, the cavity including a reference pin root shoulder located within the strainable portion of the fastener; a reference pin having a root end and a reference end, the root end of the reference pin being fixed to the reference pin root shoulder in the cavity and the reference end of the reference pin including a reference datum ; and either a) a strain datum on an outer end of the alignment protrusion , or b) a strain datum sleeve having a strainable portion datum shoulder contacting end and a strain datum end, the strainable portion datum shoulder contacting end for contacting a strainable portion datum shoulder included in a bore in the cavity and located within the strainable portion of the fastener , the strain datum end including a strain datum , the fastener being characterised in that the alignment protrusion has an engagement portion having an engagement width perpendicular to an axial engagement length , the axial engagement length being at least 0.9 times the engagement width or at least equal to the square root of a cross-sectional area for non-circular outer profiles and the engagement width of the alignment protrusion has a tolerance of no wider than ISO 286-1:2010 c11. a first load receiving portion and a second load receiving portion ; a strainable portion between the first and second load receiving portions; a measuring end including an alignment protrusion ; a cavity extending from the measuring end of the fastener, the cavity including a reference pin root shoulder located within the strainable portion of the fastener; a reference pin having a root end and a reference end, the root end of the reference pin being fixed to the reference pin root shoulder in the cavity and the reference end of the reference pin including a reference datum ; and either a) a strain datum on an outer end of the alignment protrusion , or b) a strain datum sleeve having a strainable portion datum shoulder contacting end and a strain datum end, the strainable portion datum shoulder contacting end for contacting a strainable portion datum shoulder included in a bore in the cavity and located within the strainable portion of the fastener , the strain datum end including a strain datum , a) a strain datum on an outer end of the alignment protrusion , or b) a strain datum sleeve having a strainable portion datum shoulder contacting end and a strain datum end, the strainable portion datum shoulder contacting end for contacting a strainable portion datum shoulder included in a bore in the cavity and located within the strainable portion of the fastener , the strain datum end including a strain datum , the fastener being characterised in that the alignment protrusion has an engagement portion having an engagement width perpendicular to an axial engagement length , the axial engagement length being at least 0.9 times the engagement width or at least equal to the square root of a cross-sectional area for non-circular outer profiles and the engagement width of the alignment protrusion has a tolerance of no wider than ISO 286-1:2010 c11. <EOS>