Abstract: A modular wrench has a shaft, a connecting protrusion and a socket mount. The shaft has two ends and two sides. The connecting protrusion is formed on and protrudes from one side at one of the ends. The socket mount is attached to the other end of the shaft, may be mounted in or formed on the same or opposite side and has a mounting hole formed in the socket mount. The socket mount can be combined with the connecting protrusion of another modular wrench to extend length or adjust configuration of the modular wrench. A socket is mounted in a distal socket mount corresponding to and for tightening or loosening fasteners. Therefore, the modular wrench can be easily adapted to work fasteners of machines.