Screwdrivers

Screwdrivers are used to increase the torque you can apply to a screw by providing a large diameter and textured grip rigidly connected to a hardened shank with a driver ground into the end.

Types of Screwdrivers

Screwdrivers are available in a variety of shapes to allow access to screws in almost any possible orientation with many different clearances. Some screws may be buried deep in a recessed hole, requiring a long shank, while others may have almost no vertical clearance and require an offset screwdriver.

• Normal - The normal screwdriver has a shank whose length is roughly proportional to the size of the driver. These are the most commonly used screwdriver and should be the first thing you reach for.

• Extended - The long shank of the extended screwdriver lets you reach screws that are in deep pockets or across large enclosures.

• Stubby - For screws that have less vertical clearance, such as those in recessed cavities or inside enclosures, a stubby screwdriver is often used. These short shanked tools often have large handles and are likely the second most common form factor.

• Offset - In some cases, screws have almost no vertical clearance. An offset screwdriver has a right angle bend and can be used to access such screws.
• Ratcheting - To increase how fast the user can turn the screw, some screwdrivers are equipped with a ratcheting mechanism. These are very useful, but should not be used for high-torque screws and they ratchet mechanism can become stripped.

Types of Drives

There are many types of drives, so many that it is really impossible to cover and not worth covering as you will commonly only encounter a few drives. Many drive types have been introduced by manufacturers to prevent tampering, others are used in certain niche applications only. A relatively comprehensive list of screw drives is available in a Wikipedia article.

• Slot - The first drive developed. It has been traditionally the most common because of its low cost of manufacture. Slotted screws are not common on anything that a power tool will be used on, as the blade slips out of the slot very easily. This could be dangerous to the part’s finish and any nearby skin. You may hear this drive referred to as the common blade, standard, flat-blade, or flat-head drive.

• Phillips - This screw drive was dismissed by manufacturers in the 1930’s, but has since become a very common drive. The cruciform nature of the phillips makes registering the driver into the screw easy and the blade cannot slip off the end of the head like common head screws. The Phillips does have a tendency to “cam out” at high torques. The bit will force itself up and out of the slots, possibly stripping. Other drives such as the PoziDriv were developed to combat this, but the Phillips is still commonly found in many applications. It is easy to confuse the Phillips with the very similar Fearson drive. Phillips drives have a blunt tip opposed to the sharp tip of the Fearson drive.

• External - External drives reverse the roles of the driver and screw head. The driver slips over a protruding pattern on the screw head, often square or hex. These provide a lower vertical clearance, but are much easier to tighten to high torques than common or Phillips drive screws.

• Torx - Torx is a trademarked name for a 6-point star shaped drive, generically referred to as the ISO10064 hexalobular internal drive. Torx provides a very good mechanical connection and can work in low vertical clearance situations.

• Hex Socket (Allen) - Similar to the external hex drive, the hex socket drive, commonly referred to as the Allen drive consists of a hexagonal pocket into the screw head and a hex shaped driver that fits into the “socket” head. This type of drive proves excellent mechanical connection and is often used in scientific equipment assembly.

Use

To use a screwdriver, first double check that you have the appropriate sized driver for the fastener you need to remove or install. Using the wrong sized tool will likely damage the fastener and make it difficult or impossible to remove. Insert the driver into the fastener and press straight down firmly. Turn the screwdriver clockwise to tighten or counter-clockwise to loosen a regular right-handed thread fastener. Occasionally you will encounter left-handed threads that are the opposite to this. As a rule of thumb, remember “righty tighty, lefty loosey.”

Screwdrivers are often used as pry bars, scrapers, or chisels, but they were NOT designed for these tasks. Improper use will damage the tip, bend the shank, and likely end in injury. A damaged screwdriver will then likely strip the screw it is used on next and create a cascading event of damaged hardware. Never use a chipped, bent, or otherwise mangled screwdriver.

Safety Precautions

The main safety hazards associated with screwdrivers are puncture wounds when the tool slips out of the screw head. Improper use of the driver, as a pry bar for example, could result in fracture and flying metal chips.