Probably the most common of all fastener heads, hex heads are also very old. To find the size of wrench needed to turn a hex head or hex recess , measure from flat to flat, not from point to point.
Socket wrench sizes for some common machine screws and bolts are given in the table. Sizes are the flat-to-flat dimension. For lists of inch and metric allen key sizes, and the set screws and cap screws they fit, see this page. The common 8-pt double-square socket wrench does not fit an octagonal head. True octagonal socket wrenches are made, but are rare. Originated by United Screw and Bolt.
The recess in clutch heads looks like a bowtie. In a pinch, a clutch head screw can be driven by a slotted screwdriver. A worn tip on a driver can easily be restored by grinding off the end. Clutch head screws were popular in mobile home construction and electric motors. Originated by the Bristol Co. A recess with 6 flutes except for 2 sizes that have 4 flutes. Sized in inches:. The Torx system was introduced in by Camcar, and patented in Its great popularity, however, really began in the 's, when it became very common in trucks and automobiles.
Both internal and external versions are made. The walls of the recess are not tapered, so camout is absent. Drivers greatly outlast similar hex head drivers. The same system of sizes is used for both metric and inch fasteners. To match drivers to fastener sizes, see the table below, under Torx Plus. Driver sizes for Torx recesses begin with a T. The dimensions below are measured on the driver bit, from point to opposite point.
Tamperproof Torx heads are the same as the internal recess heads, but have a post in the center which prevents ordinary Torx drivers from entering the recess. The Torx Plus system was introduced by Camcar in Like Torx, it is 6-lobed and has straight walls. The improvement is in the design of the lobes, which were changed to elliptical from circular in Torx.
The result is that the force imparted by turning the driver is perpendicular to a radius of the fastener. A Torx driver can drive or remove a Torx Plus screw, but the added benefits of the Torx Plus design are lost and wear is increased. If you are reading this on a smartphone, the next table will be wider than your screen. To avoid having to scroll horizontally, please turn your device horizontally and view the table in landscape mode.
Tamper-resistant Torx Plus recesses differ from other Torx Plus recesses in having 5 lobes instead of 6. It also has a center post. The usual strategy for creating such screws is to add a post in the center of the recess in the screw head, and a central hole in the driver. The post prevents the ordinary driver from entering the recess. The TT Torx screws are an example of such a system. However, today anyone can buy drivers to fit such security screws, on the web, if not in the local hardware store.
Like the Phillips screwdrivers, Robertson drives also make use of a numbering system. Robertson drives have corresponding color codes to make each size easy to identify.
The Phillips screwdriver has become the standard in many different countries. Phillips screwdrivers can be used on many different cruciform screws. Torx drives are designed to function at higher torques than other screwdriver types and also have a longer lifespan.
A Pozidriv bit will not fit inside a Phillips fastener. Hex keys are named because they have a smooth hexagonal shank and no head.
More commonly referred to as Allen wrenches , these screwdrivers sometimes come in an L-shaped shank with no handle, as multiple retractable sizes with a centrah handle ala Swiss army knives , or even with a ball-shaped tip. Measurements for hex keys is done via AF short for across flats. To measure an unmarked key, for example, you would measure the distance between two opposing ends. Popular in both construction and electrical fields, the Robertson drive commonly referred to as the square drive is more common in Canada than the US due to licensing problems earlier in its history.
Now that the original patents and licensing restrictions have begun to expire, Robertson screws are gaining in popularity worldwide. Much like Phillips screwdrivers, Robertson drives use a numbering system. What sets these apart, however, is that all sizes are also color-coded for easy reference. Sometimes referred to as the star drive due to its rounded 6-point star shape, the Torx drive is designed to function at higher torques and have a longer lifespan than other popular screwdriver types.
This has made them quite popular in both electronics and automotive industries. Torx drives use a numbering system based upon the distance between two opposing points. Unlike other driver measuring systems, the same numbers on a Torx screwdriver apply to both SAE and metric scales. You can identify the size required for a random screw by measuring the width of the slot and comparing it to a Torx sizing chart.
What is the M2. Being Canadian having worked with every type of screw out there Robertson are are far and away the best ans seem to be the fastest way to go. It looks like Torx but has a knob in the centre of the screw. So far only seen small ones. Thanks for the charts and mentioning colour coating. Actually a great idea. It just seems easier to look for a green or a red rather than searching for size.
You are correct about Torx being invented by an auto manufacturer; General Motors, in fact. They were a cheaply made screwdriver-style with two sizes available.
Oh for a world full of Robertson heads and the drivers of course. Thanks again!! I concur!!! I have been looking everywhere with no success either! Any help would be greatly appreciated! I appreciate your site as I am trying to make up a set of as many complete sets of drivers complete with individual handles permanently attached as a gift for my son. I have been in the electrical and basic electronic trade since as an apprentice tradie anl later in my own small business in which I apprenticed my own two sons, working in industry then after CABGs surgery and a stroke as a teacher.
Thanks for the comment Bill. What a fantastic gift idea for your son.
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