Abstract: A depth adjuster for a rotary tool such as a screwdriver having a tool bit projecting through a nose provided at the front end of the rotary tool. The depth adjustor comprises a locator sleeve mounted on the nose to project on the front end of the tool in such a manner as to surround the tool bit. The locator sleeve has an internal thread engaged with an external thread on the nose so as to be axially movable relative to the nose and the tool bit as the sleeve rotates about the nose. A lock ring is fitted on the nose to be rotatively fixed but axially movable relative thereto. The lock ring is biased towards the locator sleeve by a spring for locking engagement into the locator sleeve so as to rotatively fix the locator sleeve around the nose, whereby retaining the locator sleeve at a desired axial position relative to the nose.