Types of Screw Heads/Screw Drives





Introduction: Types of Screw Heads/Screw Drives

About: Occupation: Tech Support

Quick primer on some of the more common types of screwdriver heads for use in various projects. Please note that this is by no means comprehensive, but is designed to explain the more common types in use for woodworking and computers.

Step 1: Slotted

Slotted screws are the simplest type of screw, consisting of a single slot at the head of the screw. Generally not in heavy use in the US, but they are still around.

Flat head screwdrivers and driver bits (which are used for slotted screws) are measured by the width of the blade in inches, eg: 1/16, 1/8, 1/4, 5/64, 3/16, 3/32, 5/32, 9/32.

When discussing slotted screwdriver bits, sometimes the designation "SL" is used.

Step 2: Phillips

The Phillips screw, named after Henry F. Phillips, was purposely designed to "cam out", or have the screwdriver come out after putting too much torque on the screw. This was an intentional engineering point, since at the beginning of the 20th century, machine tools were generating high amounts of torque that were breaking screw heads off. With the Phillips, the extra torque would cause the driver to pop out, preventing the screw head from breaking off and making production line assembly go more quickly. Personally, I am not a big fan of using Phillips for woodwork, but they are in wide use in the US for both wood and computers, so it is important to include them.

Phillips head screwdrivers and bits are denoted by the abbreviation "PH" and the size in numbers, eg: PH #00, PH #0, PH #1, PH #2, PH #3. "PH #00" is small (used for computers), "PH #3" is large.

Step 3: Square Aka "Robertson"

The Square head screwdriver (also known as "Robertson"), was invented by Peter L. Robertson, a Canadian. It is the most common screw in Canada today (Hail Canada!), but it is also sold in the US. In my opinion, it is far superior to the Phillips, since it allows the driver to go deep into screw head, allowing the user to generate more torque than is possible with the Phillips. The shape and depth allows 4 solid points of contact, and as such is designed to *not* cam-out. Another benefit of Square heads is that since they do not strip, it is easy to back the screw out in case it is necessary.

The sizes of square drivers are designated by "SQ", eg: SQ #0, SQ #1, SQ #2, SQ #3. "SQ #0" is the smallest, "SQ #3" is the largest. Often boxes of Square head screws will come with Square drive bits, usually SQ #2.

A common brand of Square head screws is Backer-On. One company that makes Square head screws, Spax, makes screws that can use either a Square head or Phillips driver. These are great to use since they give you a choice (when I use them I always use the Square head portion.)

Step 4: Torx Aka "Star"

Torx screws, first developed in 1967 by Camcar/Textron in the US, are also known as "star" or "hex" screws. (The official ISO name is "hexalobular internal".) They are similar to Square screws in that it allows the driver to go deep into the head, except that instead of having 4 points of contact like the Square, it has 6 points of contact. As such, this makes it, in my opinion, superior to the Square, and much more superior than the Phillips. Like the Square, the Torx is designed to *not* cam-out and to allow the user to generate more torque when screwing it in. The Torx allows the user to generate so much torque that it is possible to break the head off (I did this once using a hand screwdriver on a wood project). This torque comes in handy when using more dense wood, like maple. With less dense wood, like pine, the extra torque is great for creating a solid connection between the 2 pieces of wood and being able to countersink the screw.

Somewhat more expensive than Phillips, but in my mind, it is worth the money, particularly when woodworking. Common brands include GRK, Hillman and Grip-Rite. The sizes of Torx screws and drivers are designated by a "T" and a number, eg: T7, T8, T9, T10, T15, T20, T25, T27, T30, T40. "T7" is the smallest and "T40" is the largest.

Please note that most Torx screws come with the correct size Torx bit in the box, usually a T20 or T15. Another benefit of Torx heads is that since they do not strip, it is easy to back the screw out in case it is necessary.



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    19 Discussions


    1 year ago

    i.e. flat pan head with slotted drive

    1 reply

    Good catch. Will update. Thank you.


    1 year ago

    Slotted is not a head, its a drive.

    Wish I had seen this last week. Now that I have though I won't be so indecisive when I am at the Hardware store or asile! Thanks for the lesson.

    1 reply

    You're welcome! Hope it helps in the future. My preference is for Torx screws.

    Thank you - interesting resource!

    What about socket head screws (also known as "Allen Head" screws in the US)? While many of their uses have been replaced by Torx, they are still very popular in machinery and military equipment.

    There is also the tamper-resistant Torx - it has a pin located in the middle of the star pattern (and the driver has a small hole drilled in the middle of the driver bit).

    1 reply

    Honestly, I do not have that much experience with those types of screws. And being a pacifist, it is my feeling that it would be best to share information about what is used in the civilian world so that the people in the military can be prepared for life after they get out of the military.

    could you go over the different head shapes and what they do. I have figured out a lot on my own, however my tool education has been very limited. What you have already done is awesome, and extreamly useful. No wonder I get so frustrated with the phillips heads.

    1 reply

    The Phillips can be frustrating when working with wood. That is why the Square and Torx are excellent solutions.

    A very good write up. Although less reliable when driving in high torque situations, the Phillips head does have merit with a cam- out feature, especially in the drywall screw category. It is less likely to be overdriven and is quick to disengage when proper countersink depth is reached. I do however, prefer Robertson and Torx designs for most other uses.

    2 replies

    That is a good thought; drywall can be quite soft when drilling, so too much torque might cause it to drive too deep in. Countersinking is good, but if it goes down too far it will loose its hold on the drywall.

    Thank you for the compliment!

    You should probably cover the differences between Phillips and posidrive.

    Also as a side note for Robertson screwdrivers. They are colour coded with either the handle or a stripe on the handle being a colour that references the size. The #0 is always yellow #1 is green #2 is red and #3 is black. I have put coloured markings on my Phillips screw drivers using the same colour code for easy identification in the tool tray.

    I personally prefer Robertson screws for woodworking.

    2 replies

    Excellent point - thank you! I will start to research the Pozidrive.

    Great color coding system - sounds like you are quite efficient.

    Robertsons are great for woodworking too; after using Torx and Robertsons, it is almost impossible to go back to Phillips.

    See http://www.thomasnet.com/articles/hardware/robertson-screwdriver-history

    never seen Robertsons in the UK. I think as long as you're not turning them too hard so you start to round off the square shape or upper edges they'd look pretty cool left exposed, especially if you went to the effort to align them all the same way so the squares were all horizontal

    1 reply

    Very interesting! I didn't even think of Robertson screws as a design statement, but it is a good idea.