Abstract: A wrist instrument has an expandable strap for use in securing the instrument about a wearer's wrist. The expandable strap has a strap casing or a sheath on each end and an interconnecting member attached to the strap casings. The interconnecting member includes a non-expandable section and at least one elastic member housed in one of the strap casings. The elastic member is attached to both the strap casing housing it and the non-expandable section of the interconnecting member such that when a pulling force is exerted on the interconnecting member, the elastic member expands within the strap casing to allow the strap to accommodate different wrist sizes without exposing the elastic member to view.