FASTENERS 101™
Drives, Heads and Threads
Fastener Specifics
Drive Styles
These are some of the most popular drive styles that screws and bolts are available in. There are several more drive styles available, these are the styles that you will currently find on our site:
Phillips
The most common drive style. Shaped like a cross.
Slotted
A straight line cut into the center of the head.
Slotted/Phillips Combo
A drive style combining the two most popular drives for ease of use with whatever tools you have available.
Square
A square shape, resists stripping out.
Star (Torx, 6-Lobe)
Torx drive, also known as star drive resists stripping out and provides a more decorative drive finish.
Pin-in Star (Torx Tamperproof)
Torx with pin security drive can only be driven with security bits and are used to prevent tampering and theft.
Hex (Allen, Socket)
Driven with an Allen Key, hex wrench or socket driver, socket caps are often used for decorative or automotive applications.
Pin-In Security Hex (Allen) Socket
also known as tamper-resistant hex, security Allen, or vandal-resistant hex—has a center pin and requires a matching pin-in hex/Allen key or security hex bit.
External Hex Head
While not technically a drive style, the hexagonal head is designed to be driven by a wrench or socket.
One Way Security
The one-way security drive style is driven in using a flat head screwdriver and cannot be easily removed.
Spanner Security Drive
Driven using a special two-point bit, also referred to as a snake eye drive.
Head Types
Bugle Head
A Bugle Head is similar to a flat head. This screw has a rounded section that will pull down the material instead of cutting through it as it is fastened. Distributing the pressure over a larger surface area.
Button Head
A button head is a rounded head, used primarily in socket cap screws. This head sits above the installation surface.
Button Flange
The button flange head is like the regular button head style but with a flange or integrated washer to increase surface area during an installation.
Dome (Cup) Head
The cup head is seen almost exclusively on carriage bolts. With a square neck, this head style is made to be pulled into soft material, such as wood, and hold the bolt in place.
Fillister Head
A head with a higher profile than a round head or button head. This type of screw also has a deeper drive area and is commonly used in countersunk holes.
External Hex Head
External hex heads are the standard bolt head. This head is designed to be driven by a wrench and allows for high torque installations.
Hex Washer Head
A head that is designed to be driven by a wrench with an integrated washer or flange to increase the installation surface area.
Knurled Cap
A knurled cap head style sits above the installation surface and has indents on the sides to be gripped by the thumb.
Knurled Thumb
A knurled cap head style sits above the installation surface and has indents on the sides to be gripped by the thumb.
Smooth Cap Head
Like a knurled cap head style but designed to be driven by an Allen wrench or hex key. The smooth sides give it a cleaner finished look.
No Head
The head of a socket set screw, lacks a head and has an internal drive in the body of the screw itself. Designed to sit flush with the installation surface.
Flat Head
A flat head is can have several drive styles, designed to be drilled into a material until it sits flush with the installation surface.
Oval Head
Similar underside to that of a flat head screw but with a decorative rounded top. Commonly used as a finish screw in visible applications.
Pan Head
A screw with a rounded head (less so than a button or round head) and a flat bottom designed to sit directly on the installation surface.
Pancake Head
A flat-topped screw with a wide head to sit close to flush but also have a large surface area on the installation material for grip.
Round Head
A completely rounded head that was very popular but has become less so with the variety of heads now available.
Square Head
A head designed to give better grip to a wrench than an external hex head.
Truss Head
With a flat bottom and a wider installation surface area, this screw is used where a lower profile is desired, but a strong grip is needed.
Modified Truss Head
Like the truss head but with an integrated washer which increases the surface area of the head even more.
Thread Types
COARSE THREAD - UNC
Coarse threads are those with larger pitch (fewer threads per axial distance) and larger thread form relative to screw diameter. Example: 5/16-18. This screw has 18 threads per inch.
FINE THREAD - UNF
Fine threads are those with smaller pitch (more threads per axial distance) and a smaller thread form relative to screw diameter. Example: 5/16-24. This screw has 24 threads per inch.
Coarse Thread Vs. Fine Thread
Coarse threads have higher thread peaks than fine threading. These threads are more durable. With a greater resistance to stripping and less need to handle them gently, coarse thread fasteners are more readily available than fine thread. They are also less susceptible to thread galling than fine thread.
Fine threads are stronger than their coarse thread equivalents. They are also much less likely to be shaken loose during vibration due to their tighter helical structure. Fine threads are also less commonly used and require more care to avoid stripping and cross-threading. Due to the increased number of rotations they require to install, they are also more likely to encounter galling upon installation. Anti-Seize Solution is recommended.
Preventing Fastener Drive Stripping (Stripped Screws)
There are many different drive styles available today that have improved the way screws are driven. Unfortunately, none are without flaws. Follow these guidelines to prevent your screws from stripping when installing or removing fasteners.
- Ensure the driver is the correct size. If the driver does not fit fully into the drive recess, change the size.
- Check the driver for damage due to over-use or mis-manufacturing. If it is not perfect, it is more likely to cause stripping. Replace the driver.
- Make sure the drive is set fully into the drive recess. If the driver is angled, it will apply uneven torque and likely damage the drive recess.
- Drill pilot holes in harder materials. Otherwise, the fastener may heat up and seize which can cause stripping or snapping to occur.
- Make sure to drive smoothly and evenly until the fastener reaches the desired stopping point. Do not over-tighten as this may cause excess torque to be applied to the drive and cause snapping or stripping as well.
- In scenarios where both metric and standard drive sizes exist (external and internal hex) make sure the correct size is used. Most sizes do not correlate directly and the gap between the fastener and drive may cause rounding or stripping to occur.
*Note: The Phillips drive style should not be used in high torque applications. It is more likely to cam out and another head style should be used.