Torque Driver
Also: FAT Wrench · Torque Wrench
A handheld tool that tightens fasteners to an exact, repeatable torque, used on rings, bases, and action screws to protect zero and grouping.
A torque driver is a screwdriver or wrench that lets you set a target value and then clicks, slips, or reads out when the fastener reaches it. Precision shooters use one because guessing at how tight a screw should be is one of the quietest sources of trouble on a rifle. Following the published torque-spec for each fastener keeps clamping force consistent, which is what protects both the optic and the gun from uneven stress.
The most common uses are mounting scope-rings and a scope-base, where uneven ring screws can pinch the tube or let the scope creep under recoil. Action screws into the stock or chassis matter just as much, because inconsistent bedding tension shows up as wandering groups. Torqueing every fastener to the same number each time is also what makes a reliable return-to-zero possible after the optic comes off and goes back on.