American Machine Screw Size and Diameters Chart with Complete Question

Cap and machine screws are used to clamp machine parts together, either when one of the parts has a threaded hole or in conjunction with a nut. These screws stretch when tightened, and the tensile load created clamps the parts together. The setscrew fits into a threaded.

There are two major screw thread systems used to classify machine screws. The Unified Screw Thread System is most commonly used across the U.S. and Canada. Here we will define the details machine screw size and diameters.

US Machine Screw Size Diameters

Size Recommended Torque
Grade 2 Grade 5 Grade 8 18-8 S/S Bronze Brass
Coarse Fine Coarse Fine Coarse Fine Coarse Fine Coarse Fine Coarse Fine
#4* 5.2 4.8 4.3
#6* 9.6 8.9 7.9
#8* 19.8 18.4 16.2
#10* 22.8 31.7 21.2 29.3 18.6 25.9
1/4″ 4 4.7 6.3 7.3 9 10 6.3 7.8 5.7 7.3 5.1 6.4
5/16″ 8 9 13 14 18 20 11 11.8 10.3 10.9 8.9 9.7
3/8″ 15 17 23 26 33 37 20 22 18 20 16 18
7/16″ 24 27 37 41 52 58 31 33 29 31 26 27
1/2″ 37 41 57 64 80 90 43 45 40 42 35 37
9/16″ 53 59 82 91 115 129 57 63 53 58 47 51
5/8″ 73 83 112 128 159 180 93 104 86 96 76 85
3/4″ 125 138 200 223 282 315 128 124 104 102 118 115
7/8″ 129 144 322 355 454 501 194 193 178 178 159 158
1″† 188 210 483 541 682 764 287 289 265 240 235 212

US Machine Screw Threads Diameter

THREAD DIAMETER
Size Nearest Fraction Inch Millimeter
#0 1/16 0.06 1.5
#1 5/64 0.07 1.8
#2 3/32 0.08 2.0
#3 7/64 0.09 2.3
#4 7/64 0.11 2.8
#5 1/8 0.12 3.1
#6 9/64 0.13 3.3
#8 5/32 0.16 4.2
#10 3/16 0.19 4.8
#12 7/32 0.21 5.5
#14 1/4 0.24 6.3

  Q: Is a machine screw a bolt?

Ans: Machine screws may look like bolts, but they aren’t necessarily the same. Machine screws have a slotted head, whereas bolts have a hex head. With a slotted head, machine screws can be installed using a screwdriver, such as a Philips head or flat-heat screwdriver.

Q: What is the difference between a machine screw and a bolt?

Ans: Bolts tend to be driven home and then tightened fully by turning the nut on the rear side of the fastening. With machine screws, the majority of tightening force (torque) is applied to the head of the screw itself when driving it into a tapped hole.

Q: Are machine screws tapered?

Ans: Machine screws have a uniform diameter the entire length of the shaft as opposed to tapered screws which have a pointed tip. They are used to fasten machine components, appliances and more.

Q: Are machine screws strong?

Ans: Since machine screws are used for holding together engines, electronics, and industrial equipment, they are extremely strong. While quality screws, in general, are pretty strong, these are extra strong as they have much heavier items to hold together.

Q: What are machine screw sizes?

Ans: Machine screws are often found in sizes of: 0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14—the larger the number, the larger the screw. Machine screws, but especially caps screws and bolts, can range from 1/4 inch up to 3 inches or more.

Q: What diameter is a #12 machine screw?

Ans: 

Size Nominal Thread Diameter
Decimal Nearest Fractional
#12 0.216″ 7/32″

Q: What diameter is a number 8 machine screw?

Ans: A #8 screw size is . 164 fraction of an inch. The diameters listed in the chart below are in fractions of an inch, so the #12 is just shy of 1/4 inch. A more detailed table with thread count can be found below, along with tap drill sizes.

Q: What are standard screw sizes?
 
Ans: The main difference between 10-32 and 12-24 threads is their dimensions. 10-32 screws have a diameter of 3/16″ (4.8mm) where as 12-24 screws have a diameter of 7/32″ (5.6mm). M6 threads are 6mm in diameter, only . 4 mm larger than 12-24 screws.
 
Q: What is a #8 screw size?
 
Ans: A #8 screw size is . 164 fraction of an inch. The diameters listed in the chart below are in fractions of an inch, so the #12 is just shy of 1/4 inch.

Q: Is a #8 screw the same as M8?

Ans: Well, quick answer is no. They are not the same and they are not interchangeable, although they can work under certain circumstances. The most important part is understanding the meaning of M8 and 5/16 to refer to the size of a metric screw or bolt, so then we can see why they aren’t the same thing!

Q: What does a 10 24 screw mean?

Ans: The first definition is about the size of the screw. For a 10-24 screw this is 0.19 of an inch as the major diameter and 0.1379 as the minor diameter.

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