Abstract: A torque limiting wrench which has a marking mechanism to mark a part that is tightened by the wrench at the instant the intended torque has been applied to the part. The wrench includes an elongated torque applying handle, a cylindrical housing mounted at one end to the torque applying handle, a replaceable part engaging head assembly releasably mounted to the other end of the cylindrical housing, and a part marking mechanism mounted within the cylindrical housing. An on-off valve unit, associated with the torque applying handle, is actuated in response to the desired torque level being reached to operate the marking mechanism by which a mark is applied to the part simultaneously with the interruption of torque transmission. The head assembly is releasably retained to one end of the cylindrical housing such that an operator may simply and conveniently replace any head assembly with another one of a different size or design.