A multiple-in-one socket includes a socket body having a first gradational cavity recessed in a first end of the socket body, and a second gradational cavity recessed in a second end of the socket body opposite to the first gradational cavity; each gradational cavity including a plurality of polygonal holes gradationally contracted in sizes inwardly from an outermost hole towards an innermost hole; whereby a plurality of polygonal holes having plurality of hole sizes may be conveniently chosen for fastening a bolt or nut by correspondingly matching the bolt (or nut) size with the polygonal-hole size.