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Tightening fasteners to the specified torque is not only safe but the right thing to do. In fact, safety and installation inspectors measure the torque on fasteners to ensure they are installed correctly. It is very easy to apply and measure torque on nuts and bolts. All you need is a torque wrench and the right size of a socket. With screws, however, it is a little bit different and can be difficult. Unless a screw head has an external hex shape to let you use a wrench or spanner.
Most screws have a rounded head and a drive for inserting the screwdriver tip. Accordingly, there are more than a dozen types of drives. That is why screwdriver head tips come in different shapes including the flathead or slot, Phillips, Torx, positive, internal hex, and so on.
How to torque screws without overtightening and undertightening
To install or remove screws, you can use either a hand screwdriver or power tools such as a drill or impact driver. However, as I have mentioned, torquing screws to specification is not a straight foward activity. Not only do you need a torque wrench and socket, but also a screwdriver with a proper handle. When I say a screwdriver with a proper handle, I mean a screw driver handle that is designed for use with wrenches or sockets. Otherwise, it may not be possible to use your torque wrench to measure the amount of torque applied on a screw fastener.
Screwdrivers for use with wrenches have grooved or ridged plastic or metallic handles. These types of handles allow a wrench or socket to slide over so that you can apply more axial pressure for tightening or loosening screws.
More importantly, you can also use a torque wrench on a ridged screw driver handle to tighten screw fasteners to the specified torque. This is the little know secret about why screwdrivers have ridged plastic handles.
What you need to know
Before using a torque wrench, box-end wrench, or ring spanner on a screwdriver, you need to know the following:
1. Size of the screwdriver handle
Screwdriver manufacturers do not label the size of the grooved handles. So, trial and error is the easiest way to determine the size of the wrench that would fit. If you have a wrench set, spanner set, or socket set, you can try each size until you find the one that fits snugly. Once you establish the right size, label the handle to make it easier to pick the right one next time.
2. Type of screwdriver handle
Not all screw driver handles are shaped for use with wrenches. Only the grooved handles allow a spanner to slide over. Mostly, those ridged handles are made of hard plastic. This makes them withstand stress to prevent rounding off.
3. Torque specification
Some screws such as wood screws and machine screws have very fragile heads. They can easily be stripped by too much torque. Since a wrench on a screwdriver allows you to apply extra axial pressure on a screw, it is good to know how much torque you need to avoid stripping the screw head.
Sometimes you might even damage the tip of your screwdriver when you apply too much torque. Different screwdrivers are designed to handle different amounts of torque. So you need to be very careful when using a wrench as leverage for your hand screwdriver.
In a nutshell, when selecting a screwdriver, do not just look at the shape of the tip. It is also important to look at the shape of the screwdriver handle. If you need to tighten screws to a specified torque value, you need a screwdriver with a grooved handle. Such screw drivers do not provide the most comfortable grip but let you slide over a box-end wrench or socket.