It is very strenuous to fasten and dismantle large diameter bolt vice and very difficult to control its moment precision manually under installing the heavy-duty equipment in such trades as electricity, petroleum, machinery, traffic and shipbuilding, etc. FDB series manual torque multipliers can enlarge input moment 4-40 times to obtain large definite value moment, finish fastening or dismantling nut and bolt lightly, and can guarantee advanced tight force of a set of bolts unanimously. It is especially suitable for narrow operation space or electricity- forbidden occasions.