A mechanical fastener assembly is provided for joining two or more workpieces. The assembly includes a mechanical fastener and a slotted insert. The mechanical fastener has a shaft received within aligned bores of the workpieces. The slotted insert surrounds at least a portion of the shaft and has a body portion received within the aligned bores, while an enlarged head portion of the slotted insert is positioned outside of the bores. The mechanical fastener assembly may further include a retaining sleeve when the bores of the workpieces have different diameters. In such case, a midsection of the retaining sleeve is at least partially received within the bore having the smaller diameter, while an enlarged end section of the retaining sleeve is at least partially received within the bore having the greater diameter. The retaining sleeve may be used in combination with or independently of the slotted insert.