Abstract: An airline lubricator is disclosed with a tamper-proof, oil-metering adjuster provided for adjusting the quantity of oil delivered by the lubricator, and for preventing tampering or accidental readjustment. The tamper-proof construction for a selectively adjustable screw controller includes a lock therefor wherein an elongated, rotatable, screw controller is provided with a splined portion, and the stationary body is also splined for cooperation with an axially movable lock collar that normally engages both the splines on the controller and the splines on the body to prevent tampering or accidental readjustment, and with a removable knob-like adjuster provided to selectively move and disengage the lock collar and to then also effect selective screw adjustment of the controller. When the adjuster is removed, the device becomes substantially tamper proof.