Understanding Metric Hex Screw Sizes: A Guide

Hex screws are a type of fastening that is critical in the safe assembly of machinery, equipment, and furniture. It is important to use the right size of hex screw to ensure safety. The size of a metric hex screw is specified using diameter, pitch, and length dimensions, in millimeters. For example, an M8 bolt has a nominal diameter of 8 millimeters, while an M12-50 bolt has a diameter of 12 millimeters and a length of 50 millimeters. Drilled head metric hexagon socket head cap screws are typically available in sizes ranging from M3 to M36.

Hex screw sizes are measured in millimetres

The pitch of a bolt is the distance between threads and is also measured in millimetres. For instance, in the specification M8-1.0 x 20, the number 1.0 is the thread pitch in millimetres, and the final figure, 20, is the length in millimetres. Metric bolts with a coarse thread pitch have more threads per inch than comparable imperial bolts.

When the pitch dimension is not provided in a metric bolt specification, it is assumed to be a coarse-threaded bolt. For example, M12-50 has a diameter of 12 mm and a length of 50 mm, but the pitch is not specified, indicating a coarse thread.

Drilled head metric hexagon socket head cap screws are typically available in sizes ranging from M3 to M36. The M3 and M4 sizes have two drilled holes spaced 180 degrees apart, while the M5 and larger sizes have six drilled holes spaced 60 degrees apart, unless specified otherwise by the purchaser.

The 'M' in M3, M8, M12 refers to metric thread

The "M" in M3, M8, and M12 refers to metric thread sizes. The "M" stands for "metric" and is used in the context of threading to refer to a specific set of measurements for determining the size of a threaded fastener, such as a screw or bolt. The metric system of measurement, which uses the meter and millimeter as its basic units, forms the basis of these measurements.

The "3" in M3, the "8" in M8, and the "12" in M12 indicate the nominal diameter of the bolt's thread in millimeters. Therefore, an M3 bolt has a thread diameter of 3 millimeters, an M8 bolt has an 8-millimeter thread diameter, and an M12 bolt has a 12-millimeter thread diameter.

It's worth noting that the size of a metric fastener is more accurately specified using diameter, pitch, and length dimensions, all in millimeters. For nuts, the size dimensions used are the diameter and pitch.

For example, consider the metric bolt specification: M8-1.0 x 20. Here, the letter "M" indicates a metric thread. The number "8" refers to an 8-millimeter nominal diameter. The "1.0" represents a thread pitch of 1.0 millimeter, and the final figure, "20," denotes a length of 20 millimeters.

It is common to see metric bolts specified in an abbreviated format, such as M12-50, where the pitch definition is omitted, implying a coarse thread. When the pitch dimension is not provided in a metric bolt specification, the bolt is always coarse-threaded.

Metric fasteners are available with either coarse or fine thread pitches, and some metric bolt sizes offer extra-fine thread pitch options. Metric bolts with coarse thread pitches have more threads per inch, resulting in closer spacing than comparable imperial bolts.

Metric fasteners are available with coarse or fine thread pitches

Metric fasteners are typically classified as either coarse or fine, referring to their thread pitch. Some sizes are also available in an extra fine thread. The thread pitch refers to the distance between adjacent threads. For example, a pitch of 1.0 means that the distance from one thread to the next is 1.0 millimetre.

Coarse metric fasteners tend to have more closely spaced threads when compared to standard "inch" fasteners of a comparable size. Fine metric fasteners can be more or less fine, depending on their size. Coarse thread fasteners are the most common metric thread and are assumed when the pitch is not specified.

Coarse thread fasteners are beneficial when quick assembly is required as they are less likely to cross-thread. Fine thread fasteners are used in more precise applications. They have higher tension strength due to their larger tensile stress areas. However, fine thread applications require a longer engagement than coarse thread applications to ensure stripping does not occur.

The length of a metric bolt is measured the same way as an imperial bolt

Hex screws are available in both metric and imperial sizes. Metric bolts are measured in millimetres, whereas imperial bolts are measured in inches. However, the length of a metric bolt is measured in the same way as an imperial bolt.

The length of a bolt is one of several dimensions used to classify a bolt's size. Other dimensions include the bolt's diameter, thread pitch, grade, thread length, and head size. The length of a bolt is measured from where the shank meets the head to the very tip of the fastener. The shank, also known as the body or shoulder, is the threadless part of the bolt.

When measuring the length of a bolt, it is important to consider the type of bolt head. For bolt heads that protrude above the surface, such as hex bolt dimensions, the length is measured from the tip or bottom of the bolt to where the shank meets the head. On the other hand, countersunk bolts, such as carriage bolts, sit flush with the surface. For these bolts, the length is measured from the top of the head to the bottom of the threaded part, including the head height.

In addition to length, the diameter of a bolt is another critical measurement. The diameter is the width of the bolt shank and does not include the bolt head. For metric bolts, the diameter is expressed in millimetres. The defined diameter of metric bolts is slightly larger than the actual diameter. For example, an M8 bolt will have a diameter slightly under 8mm.

In summary, while metric and imperial bolts differ in their units of measurement, the method for determining the length of a bolt is the same for both systems. The length of a bolt is measured from the point where the shank meets the head to the tip of the fastener, taking into account the type of bolt head.

The defined diameter of a metric bolt is larger than the bolt shaft

Metric bolts are referenced using “M” sizes, such as M8 or M12. However, the defined diameter of a metric bolt is slightly larger than the actual diameter of its shaft. So, for example, an M8 bolt will have a shaft diameter that is slightly under 8mm. This means that the bolt will fit through an 8mm hole, but it is common practice to drill clearance holes that are slightly larger to allow for misalignment.

The size of a metric bolt is more accurately specified using diameter, pitch, and length dimensions, all measured in millimetres. For instance, an M8-1.0 x 20 bolt has a nominal diameter of 8mm, a thread pitch of 1mm, and a length of 20mm. The thread pitch refers to the distance between threads on the bolt shaft. If the pitch is omitted from the specification, as in M12-50, then the bolt is assumed to have a coarse thread.

The length of a metric bolt is measured in the same way as for imperial bolts. For socket head, pan head, button head, and hex head bolts, the length is measured from the chamfered edge to the undercut of the head, excluding the bolt head. For flat head bolts, the length includes the height of the bolt head, while for dome head bolts, the length is measured from the highest point on the curved head.

The defined diameter of a metric bolt is, therefore, larger than the bolt shaft to allow for accurate sizing and to ensure the bolt fits securely in the specified hole size.

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