# Preferred metric sizes

Use of preferred metric sizes is common in engineering designs

Preferred metric sizes are a set of international standards and de facto standards that are designed to make using the metric system easier and simpler, especially in engineering and construction practices. One of the methods used to arrive at these preferred sizes is the use of preferred numbers and convenient numbers such as the Renard series, the 1-2-5 series to limit the number of different sizes of components needed.

One of the largest benefits of such limits is an ensuing multiplicative or exponential reduction in the number of parts, tools and other items needed to support the installation and maintenance of the items built using these techniques. This occurs because eliminating one diameter fastener will typically allow the elimination of a large number of variations on that diameter (multiple thread pitches, multiple lengths, multiple tip types, multiple head types, multiple drive types, and the tools needed for installing each, including multiple drill bits (one for each different thread pitch, material, and fit combination).

## Food and beverages

Champagne bottles in various sizes, probably 200 ml, 375 ml, 750 ml, 1.5 L, 3 L, 6 L, 9 L, 12 L and 18 L.

### Liquor bottle sizes

International agreements, including 75/106/EEC,[1] specify the capacities of liquor bottles allowed in international commerce as the following 10 sizes:

• 100 ml (110 L)
• 250 ml (14 L)
• 375 ml (38 L)
• 500 ml (12 L)
• 750 ml (34 L)
• 1 L
• 1.5 L
• 2 L
• 3 L
• 5 L

In the United States, the alcohol industry switched to metric bottle sizes on October 1, 1976, abandoning the existing 38 sizes of bottles and instead adopting the following 6 sizes:[2]

• 50 mL (miniature)
• 200 mL (replaced the half-pint) (≈237 mL is a U.S. half-pint)
• 500 mL (replaced the pint) (≈473 mL is a U.S. pint)
• 750 mL (replaced the fifth) (≈757 mL is a U.S. fifth)
• 1000 mL (replaced the quart) (≈946 mL is a U.S. quart)
• 1750 mL (replaced the half-gallon) (≈1893 mL is a half U.S. gallon)

## Building construction

### System 32 furniture

Shelf where the shelf bearing holes are placed with 32 mm distances from center to center, giving flexible choices for shelve positioning.

System 32 is a standard for the design and manufacture of furniture, most commonly used in the design of cabinets, wherein the major parts (sides, doors, etc.) are available in increments of 32 mm, and shelf supports consist of columns of 5 mm holes on 32 mm centers.

### ISO 2848 basic module

Cross section of a wooden joist layer, where 6 M (or 6 modules) indicates a distance of 600 mm.

The ISO 2848 basic module is a unit of 100 mm, often represented by a single capital "M", along with 300 mm and 600 mm groupings, that is widely used for the widths of furniture in Europe.

• A standard metric (concrete) block is 190 mm wide, 390 mm long, and 190 mm high, which allows for 10 mm mortar joints in between bricks, giving a standard unit size of 200 mm square by 400 mm long.[3]
• A standard metric brick is 90 by 57 by 190 mm; with 10 mm of mortar, that produces a standard unit of 100 mm x 200 mm.[3]

## Office equipment and supplies

### ISO 216 paper sizes

ISO 216 standard specifies the A sizes of paper, including the very common A4, wherein the base size of A0 is one square meter, and the ratio between the height and width is 2, which results in all sizes of paper having the same aspect ratio.

Also related is the set of pen thicknesses for technical drawings (0.13, 0.18, 0.25, 0.35, 0.50, 0.70, 1.00, 1.40, and 2.00 mm).

## Manufacturing

### ISO 261 and 262 fastener diameters

ISO 261 defines a set of preferred metric machine screw/bolt sizes, and ISO 262 defines a subset of those; both are based roughly on Renard series as defined in ISO 3, ISO 17, and ISO 497. Given that even ISO 262 specifies a fairly large set of diameters, a much simplified set of preferred diameters was developed by one of the lead designers of ASME Z17.1 and ANSI B4.2, Knut O. Kverneland, to reduce the list to 6 preferred sizes, and another 6 intermediate supplementary sizes.[4]

Machine screws with different thread diameters
Hex key set with metric sizes from 2 mm to 10 mm according to sizes for use with ISO 262 screw sizes (except 3.5 mm for M6 internal set screw)

For each size bolt or screw and type of head, there is a corresponding size driver prescribed by various ISO standards, including:

• Internal hex drive: ISO 2936:2014 "Assembly tools for screws and nuts—Hexagon socket screw keys"[5]
• External hex drive: ISO 4014, 4016, 4017, and 4018[6]
ISO 262 sizes Internal hex
Internal hex
Internal hex
Internal hex
set screws
External hex
ISO standard
External hex
DIN standard
M2.5 2.0 mm 2.0 mm 5 mm 5 mm
M3 2.5 mm 2.0 mm 2.0 mm 2.0 mm 5.5mm 5.5mm
M4 3.0 mm 2.5 mm 2.5 mm 2.5 mm 7 mm 7 mm
M5 4.0 mm 3.0 mm 3.0 mm 3.0 mm 8 mm 8 mm
M6 5.0 mm 4.0 mm 4.0 mm 3.5 mm 10 mm 10 mm
M8 6.0 mm 5.0 mm 5.0 mm 5.0 mm 13 mm 13 mm
M10 8.0 mm 6.0 mm 6.0 mm 6.0 mm 16 mm 17 mm
M12 10.0 mm 8.0 mm 8.0 mm 8.0 mm 18 mm 19 mm
M16 14.0 mm 10.0 mm 10.0 mm 10.0 mm 24 mm 24 mm
M20 17.0 mm 12.0 mm 12.0 mm 30 mm 30 mm
M24 19.0 mm 36 mm 36 mm
M30 22.0 mm 46 mm 46 mm

For Torx bolts, there is a corresponding size driver prescribed by Acument, the designer of the Torx drive system. As of 2018, there are no ISO standards for hexalobular drive sizes.[7]

M2.5 T8 T8 T8
M3 T10 T10 T10 T8 E4
M4 T20 T20 T25 T15 T15 E5
M5 T25 T25 T27 T25 T20 E6
M6 T30 T30 T30 T27 T30 E8
M8 T40 T40 T45 T40 T40 E10
M10 T50 T50 T50 T45 T50 E12
M12 T55 T55 T55 E14
M16 T70 T60 E20
M20 T90 E24
M24 T100 E32
M30 E36

Similarly, for Torx Plus bolts, there is a corresponding size driver prescribed by Acument, the designer of the Torx Plus drive system. As of 2018, there are no ISO standards for hexalobular drive sizes.[8]

M2.5 8IP 8IP 8IP 4EP
M3 10IP 10IP 10IP 8IP 5EP
M4 20IP 15IP 20IP 15IP 15IP 7EP
M5 25IP 20IP 27IP 25IP 20IP 8EP
M6 30IP 27IP 30IP 27IP 30IP 10EP
M8 45IP 30IP 45IP 40IP 40IP 14EP
M10 50IP 50IP 50IP 45IP 50IP 16EP
M12 55IP 55IP 55IP 55IP 55IP 20EP
M16 70IP 60IP 26EP
M20 90IP 32EP
M24 100IP 40EP
M30

### ISO 1307 plastic hose sizes

Garden hose with mouthpiece

ISO 1307:2006, Rubber and plastics hoses—Hose sizes, minimum and maximum inside diameters, and tolerances on cut-to-length hoses specifies nominal diameters for four different types of plastic hoses, including "Type C", which includes the typical garden hose. Each nominal diameter specifies different ID minimum and maximum values. The nominal size is a Renard series.

Nominal Size

ID

Type C

Non-mandrel-built

ID range

Inch

equivalent

ID

min max
3.2 n/a n/a
4 3.4 4.6
5 4.2 5.4
6.3 5.6 7.2 18 in
8 7.2 8.8 14 in
10 8.7 10.3 38 in
12.5 11.9 13.5 12 in
16 15.1 16.7 58 in
19 18.3 19.9 34 in
20 19.3 20.9
25 24.2 26.6 1 in
31.5 30.2 33.4 1+14 in
38 36.5 39.7 1+12 in

### ISO 6708 nominal pipe diameter

Nominal diameter, abbreviated DN (diamètre nominal/Durchmesser nach Norm), is the designation system specified by ISO 6708 for specifying the diameter of trade sizes of metric pipework components, and is the metric equivalent to Nominal Pipe Size.[9] It is among several ISO specifications that formalize preferred numbers, and is referred to by numerous other international standards, including ISO 7598 and EN 10255. The complete set of DN values allowed by the standard are:

DN designation DN designation DN designation
DN 10 DN 250 DN 1 500
DN 15 DN 300 DN 1 600
DN 20 DN 350 DN 1 800
DN 25 DN 400 DN 2 000
DN 32 DN 450 DN 2 200
DN 40 DN 500 DN 2 400
DN 50 DN 600 DN 2 600
DN 60 DN 700 DN 2 800
DN 65 DN 800 DN 3000
DN 80 DN 900 DN 3200
DN 100 DN 1 000 DN 3 400
DN 125 DN 1 100 DN 3 600
DN 150 DN 1 200 DN 3 800
DN 200 DN 1 400 DN 4 000

The number following the DN is a nominal value that is roughly the number of millimeters of a circular feature on the connection point of the pipe, fitting, coupling, etc., but often differing by a noticeable amount. If the DN value is related to the internal bore diameter of the feature, the size should be represented by DN/ID (for Inside Diameter), and if the DN value is related to the outside diameter, the size should be represented by DN/OD (for Outside Diameter).

The relationship between DN and NPS pipe sizes are as follows. Note that the actual internal diameter varies depending on the pipe wall thickness.[10]

DN Actual OD NPS[11]
dimensionless mm dimensionless
DN 10 17.2 38
DN 15 21.3 12
DN 20 26.9 34
DN 25 33.7 1
DN 32 42.4 1+14
DN 40 48.3 1+12
DN 50 60.3 2
DN 65 76.1 2+12
DN 80 88.9 3
DN 100 114.3 4
DN 125 139.7 -
DN 150 168.3 6
DN 200 219.1 8
DN 250 273 10
DN 300 323.9 12
DN 350 355.6 14
DN 400 406.4 16
DN 450 457 18
DN 500 508 20
DN 600 610 24
DN 700 711 28
DN 750 762 32
DN 800 813 34
DN 900 914 36
DN 1 000 1016 40
DN 1 200 1220 48

• Eurocontainer, a system for boxes that can be used for reusable packaging for transport and storage
• Gastronorm, a standard for professional kitchenware tray and container sizes
• ISO metric screw thread, the international standard for machine screw threads

## References

1. ^ "Application of Directives 75/106/EEC and 76/211/EEC concerning the marking and quantity control of e-marked prepackages" (PDF). Retrieved 2017-10-17.
2. ^ Cherry, Rona. "Liquor Industry Converts to Metric System". Retrieved 2018-11-29.
3. ^ a b
4. ^ Kverneland, Knut O. (1996). Metric Standards for Worldwide Manufacturing. Amer Society of Mechanical Engineers. ISBN 978-0791800416.
5. ^
6. ^ "ISO Hex Head Screw Per. ISO 4014 DIN 931 ISO 4014, ISO 4016, ISO 4017, ISO 4018". Engineers Edge. Retrieved 2023-01-24.
7. ^ "Torx Drive System" (PDF).
8. ^ "Torx Plus Drive System" (PDF).
9. ^ "ISO 6708:1995: Pipework components -- Definition and selection of DN (nominal size)". Retrieved 2017-10-13.
10. ^ "Tube Sizes - ISO" (PDF). Retrieved 2017-10-13.
11. ^ "ISO 17292:2004, Metal ball valves for petroleum, petrochemical and allied industries". Retrieved 2017-10-16.