A mechanical fastener assembly is provided for joining two or more workpieces. The assembly includes a mechanical fastener and a slotted collar. The mechanical fastener has a shaft received within aligned bores of the workpieces, while the slotted collar surrounds at least a portion of the shaft and is also received within the aligned bores. Inserting and advancing the slotted collar into the aligned bores causes the slot of the slotted collar to at least partially close, thereby causing an inner surface of the slotted collar to engage at least a portion of the shaft of the mechanical fastener and an outer surface of the slotted collar to engage at least a portion of the aligned bores of the two workpieces. Such a mechanical fastener assembly can effectively transform a bolted joint into a stronger shear joint.