Abstract: A lock for an adjustable jaw wrench of the type including a sliding jaw having a rack gear integral therewith and a rotatable gear or finger wheel in meshing engagement therewith so that by rotation of the rotatable gear, the slidable jaw may be moved toward and away from a stationary jaw for adjusting the effective size of the wrench. The lock of the present invention includes a movable component which lockingly engages both the rack gear and the rotatable gear or finger wheel thus locking these two components stationarily in relation to the body of the wrench and also locking them in stationary relation to each other.