Preferred Numbers Machinery's Handbook, 31st Edition
687
Preferred Numbers Preferred numbers are series of numbers selected to be used for standardization pur- poses in preference to any other numbers. Their use will lead to simplified practice, and they should be employed whenever possible for individual standard sizes and ratings, or for a series, in applications similar to the following: 1) Important or characteristic linear dimensions such as diameters and lengths, areas, volume, weights, capacities. 2) Ratings of machinery and apparatus in horsepower, kilowatts, kilovolt-amperes, volt ages, currents, speeds, power-factors, pressures, heat units, temperatures, gas or liquid- flow units, weight-handling capacities, etc. 3) Characteristic ratios of figures for all kinds of units. American National Standard for Preferred Numbers.— ANSI Standard Z17.1-1973 covers basic series of preferred numbers which are independent of any measurement sys tem and therefore can be used with metric or customary units. This standard has been withdrawn with no superseding standard specified. The numbers are rounded values of the following five geometric series of numbers: 10 N /5 , 10 N /10 , 10 N /20 , 10 N /40 , and 10 N /80 , where N is an integer in the series 0, 1, 2, 3, etc. The designations used for the five series are respectively R5, R10, R20, R40, and R80, where R stands for Renard (Charles Renard, originator of the first preferred number system) and the number indicates the root of 10 on which the particular series is based. The R5 series gives 5 numbers approximately 60 percent apart, the R10 series gives 10 numbers approximately 25 percent apart, the R20 series gives 20 numbers approximately 12 percent apart, the R40 series gives 40 numbers approximately 6 percent apart, and the R80 series gives 80 numbers approximately 3 percent apart. The number of sizes for a given purpose can be minimized by using the R5 series first and then adding sizes from the R10 and R20 series as needed. The R40 and R80 series are used principally for expressing tolerances in sizes based on preferred numbers. Preferred numbers below 1 are formed by dividing the given numbers by 10, 100, etc., and numbers above 10 are obtained by multiplying the given numbers by 10, 100, etc. Sizes graded according to the system may not be exactly proportional to one another because preferred numbers may differ from calculated values by +1.26 percent to –1.01 percent. Deviations from preferred numbers are used in some instances — for example, where whole numbers are needed, such as 32 instead of 31.5 for the number of teeth in a gear. Basic Series of Preferred Numbers ANSI Z17.1-1973 Series Designation R5 R10 R20 R40 R40 R80 R80 R80 R80 Preferred Numbers 1.00 1.00 1.00 1.00 3.15 1.00 1.80 3.15 5.60 1.60 1.25 1.12 1.06 3.35 1.03 1.85 3.25 5.80 2.50 1.60 1.25 1.12 3.55 1.06 1.90 3.35 6.00 4.00 2.00 1.40 1.18 3.75 1.09 1.95 3.45 6.15 6.30 2.50 1.60 1.25 4.00 1.12 2.00 3.55 6.30 … 3.15 1.80 1.32 4.25 1.15 2.06 3.65 6.50 … 4.00 2.00 1.40 4.50 1.18 2.12 3.75 6.70 … 5.00 2.24 1.50 4.75 1.22 2.18 3.87 6.90 … 6.30 2.50 1.60 5.00 1.25 2.24 4.00 7.10 … 8.00 2.80 1.70 5.30 1.28 2.30 4.12 7.30 … … 3.15 1.80 5.60 1.32 2.36 4.25 7.50 … … 3.55 1.90 6.00 1.36 2.43 4.37 7.75 … … 4.00 2.00 6.30 1.40 2.50 4.50 8.00 … … 4.50 2.12 6.70 1.45 2.58 4.62 8.25 … … 5.00 2.24 7.10 1.50 2.65 4.75 8.50 … … 5.60 2.36 7.50 1.55 2.72 4.87 8.75 … … 6.30 2.50 8.00 1.60 2.80 5.00 9.00 … … 7.10 2.65 8.50 1.65 2.90 5.15 9.25 … … 8.00 2.80 9.00 1.70 3.00 5.20 9.50 … … 9.00 3.00 9.50 1.75 3.07 5.45 9.75
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