Patent ID: 7886635

Claim:
A bolt or nut tightening device comprising the combination of a tightening assisting unit having an outer shaft and an inner shaft coupled to a planetary gear mechanism coaxially therewith and rotatable in directions opposite to each other, the outer shaft having a reaction receiver projecting therefrom sideways, the inner shaft being provided with an engaging portion engageable with a bolt or nut to be tightened, and input means coupled to the planetary gear mechanism, the outer shaft being provided with a tightening torque measuring unit, the tightening torque measuring unit comprising: a strain sensor provided on the outer shaft, a circuit board for converting the amount of strain of the outer shaft as detected by the strain sensor to an amount of tightening torque, an indicator for indicating the amount of tightening torque, a battery, a mount tubular member fitted around and rotatable with the outer shaft, and a case for accommodating the circuit board, the indicator and the battery, the case being attached to an outer peripheral portion of the mount tubular member and projecting toward the same direction as the reaction receiver, the case being so sized as to be hidden by a contour of the reaction receiver and being so positioned as to be hidden behind the reaction receiver when seen from the forward end side of the engaging portion.