The Most Complete Thread Sizes Chart Imperial & Metric

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We have discussed the basic thread terms including thread diameters, crest, root, and more definitions in the last article. Here we’ll focus on the thread dimensions explained and the standard imperial/metric thread sizes chart.

Thread Sizes Explained - How to Understand/Read Thread Dimensions

Thread sizes are given in nominal sizes, not in actual measurements. For instance, when a screw or bolt measures 5.9mm, it is called a 6mm thread. There are two common methods to write thread dimensions. 

1. Thread sizes in inches are specified by diameter and threads per inch. For example, in the screw size 10-24, the first digit refers to the thread diameter, the and second digit is threads-per-inch (TPI). When the diameter is smaller than 1/4”, the value is indicated by a number, like #1 or No.1. 

2. Thread sizes in metric are specified by diameter and pitch. The metric thread sizes are generally expressed as M2 × 0.25, the thread diameter is 2mm and the pitch is 0.25mm.

Thread Dimensions - Imperial Thread Sizes Chart

Here are two imperial thread sizes tables that define thread dimensions of coarse threads (UNC/UNRC) and fine threads (UNF/UNRF). All units in inches.

Coarse Thread Sizes

Fine Thread Sizes

Thread Dimensions - Metric Thread Sizes Chart

Here is the metric thread sizes table defines standard metric external thread size M1.6 to M18 per. ANSI/ASME B1.13M-1995. All units in mm. 

How do I figure out thread size?

Determining U.S. Thread Pitch

1. Measure an inch-long portion of the threaded area. Grab a ruler and lay it along the bolt or screw. ...

2. Count the number of threads in 1 inch. 

3. Measure the diameter and the length of the threaded area. 

4. Plug the information into a standard measurement.
   3 Easy Ways to Measure Thread

Which is bigger M8 or M12?

The size of a metric screw or bolt is specified as diameter, pitch and length, in millimeters (millimeters is abbreviated "mm").

Metric	Closest Inch
M7-1.0	1/4-28 (Smaller)
M8-1.25	5/16-18 (Smaller)
M10-1.5	3/8-16 (Smaller)
M12-1.75	1/2-13 (Larger)

What size is M12 thread?

Metric clearance and tapping drill hole sizes.

Size	Clearance Hole mm	Tapping Drill (fine pitch)
M8	9	7 mm
M10	11	9.0 or 8.75 mm
M12	14	10.5 mm
M16	18	16.5 mm