It is worth noting that there is no direct link here between the head size of an imperial screw and the gauge of that screw. It is purely coincidence that, from screw gauges 6- upwards, that the gauge is close to twice the head diameter although some sources would have you believe this is how the gauge is calculated. ISO/TC/ 1 Business Plan, 2007-03-05, Version 1.3. Table 3: The market share of each screw thread, p. 7.

There is a huge variety of types of screws and bolts available in the market that are available in different drive types, head styles, materials, sizes and thread pitch. They can be used with a range of complementary nuts and washers to prevent loosening once in place. Some of our most popular fixing categories include: Although it might seem hard to understand screw sizes, it’s actually a lot simpler than what you think. As you can see metric callouts and metric screw size charts are much easier to read and understand than imperial.

This is actually quite complicated, as was pointed out by Paul, one of our readers! Here is a more concise explanation of the relationship between gauge (imperial), diameter (metric in mm) and Head size. Don’t worry if you don’t follow this as not many people know about these relationships, let alone use them. More about Screws

The ISO metric screw thread is the most commonly used type of general-purpose screw thread worldwide. [1] They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947. [ citation needed] Set screws often do feature a head - very likely a hex fitting - but without a threadless section immediately below it (again, this is different to the length of unthreaded shank you’d typically find on a standard bolt). Because they often feature no protruding screw head in the traditional sense, true grub screws tend to be driven by means of a sunken internal recess at what is still generally referred to as the ‘head end’.The shank is the part of the screw that lies beneath the screw’s head. It can be threaded all the way to the tip, partially-threaded, or not threaded at all. 3. What Is the Difference Between Metric Machine Screw Sizes and Wood Screw Sizes? These are the basics to know when looking at screw sizes but to find out more about the thread of screws and other items you can look at Wikipedia. There’s a lot to learn if you’re interested! Metric Screw Sizes Explained Basic profile [ edit ] Basic profile of all ISO metric screw threads, where the male part has the external thread The minor diameter D min and effective pitch diameter D p are derived from the major diameter and pitch as If you need to make sure that you have the right size screw for the job, then please read on below. Metric Imperial Screw Conversion Chart

What about the thread per inch number? In this case, it means that the screw has the standard number of threads. The Only Metric Screw Size Chart You’ll Need There isn’t a noticeable difference between machine and wood screw sizes. However, the difference is in the physical characteristics. Machine screws – designed to be used with a tapped hole or interior nut thread. Available with all common head types including pan, flat, countersunk and truss. Head diameter in sixteenths is an inch X 2 ) – 2 = Gauge. E.g. 5/16 head times two equals 10, minus two equals 8. The Gauge is 8. Hex bolts – have a hexagonal shaped head and can have a full or partially threaded length, used with a tapped hole or interior nut thread.

As a handy coincidence, the Gauge (imperial) roughly equals the screw head size in millimetres. A 4 gauge screw will have a head that is approximately 4mm wide. ST – Self Tapping; These screws have a tip that will allow them to be screwed into (typically wood) without a pilot hole being drilled. This saves a lot of time!