Combination spanners have either a doubled ended traditional spanner, or a spanner and a ratchet. The old method of how you used to measure the size of a spanner used to be; the spanner size was named after the fastener size. Metric bolts and fasteners are manufactured in conformance with standards set by the International Organisation for Standardisation (ISO) and the German Institute for Standardisation (DIN). Here’s a list of the most common DIN and ISO numbers and what they describe. Descriptions of DIN and ISO fastener standards. Standard No. In addition to coarse and fine threads, there is another division of extra fine, or superfine threads, with a very fine pitch thread. Superfine pitch metric threads are occasionally used in automotive components, such as suspension struts, and are commonly used in the aviation manufacturing industry. This is because extra fine threads are more resistant to coming loose from vibrations. [8] Fine and superfine threads also have a greater minor diameter than coarse threads, which means the bolt or stud has a greater cross-sectional area (and therefore greater load-carrying capability) for the same nominal diameter.

ISO 68-1:1998 ISO general purpose screw threads – Basic profile – Part 1: Metric screw threads. International Organization for Standardization. The following table provides examples of clearance hole sizes, standard or coarse thread pitches along with fine thread pitches and their corresponding tapping hole sizes. Metric clearance and tapping drill hole sizes. Size The number 1.0 is the thread pitch of the bolt, which is the distance between threads, in millimeters.a b c ISO 965-1:2013 ISO general purpose metric screw threads — Tolerances — Part 1: Principles and basic data. International Organization for Standardization. 15 September 2013. For example, a ½” fastener fits a spanner with a ½’’ head. Metric fasteners often use a different sizing system to metric spanners, which could cause confusion, as the fastener size relates to the thread size rather than the head size. Metric Size

P = 2 tan ⁡ θ ⋅ H = 2 3 ⋅ H ≈ 1.154701 ⋅ H {\displaystyle P=2\tan \theta \cdot H={\frac {2}{\sqrt {3}}}\cdot H\approx 1.154701\cdot H} Below is a table common fastener sizes and lengths and their US (Inch) decimal and closest fraction equivalent. Below are some common spanner (wrench) sizes for metric screw threads. Hexagonal (generally abbreviated to "hex") head widths (width across flats, spanner size) are for DIN 934 hex nuts and hex head bolts. Other (usually smaller) sizes may occur to reduce weight or cost, including the small series flange bolts defined in ISO 4162 which typically have hexagonal head sizes corresponding to the smaller 1st choice thread size (eg. M6 small series flange bolts have 8mm hexagonal heads, as would normally be found on M5 bolts). [9] Diameter: the width of the bolt shank, the bolt head is not included. The defined diameter of metric bolts is actually slightly larger than the actual diameter. So an M8 bolt would have a diameter that’s slightly under 8mm. This abbreviated format omits the pitch definition which means that the bolt has a coarse thread. Whenever the pitch dimension is omitted from a metric bolt specification then the bolt is always coarse threaded. This example (M12-50) has a diameter of 12mm and a length of 50mm. Metric Thread PitchThe thread values are derived from rounded Renard series. They are defined in ISO 3, with "1st choice" sizes being from the Rˈˈ10 series and "2nd choice" and "3rd choice" sizes being the remaining values from the Rˈˈ20 series. [5] Trying to match your spanners and bolts can be a confusing and frustrating process. You hear a lot of phrases and words being thrown about, ‘M5’ this and ‘M12’ that, and you may not understand everything being said. This guide is here to help you, and hopefully give you a better understanding and put a stop to the confusion once and for all! Types of Spanners: The defined diameter of metric bolts is actually slightly larger than the actual diameter of the bolt shaft. So an M8 bolt would have a shaft diameter that’s slightly under 8mm which means that the bolt should fit through an 8mm hole. But it’s common practice to drill clearance holes that are slightly larger to allow for misalignment.