Screw Size Chart And Thread Count Guide

This post was last updated on September 10th, 2022 at 06:02 am

What is the first thing that comes to mind when you hear the word fastener? It might be nails, bolts, nuts, washers, screws, or rivets. All these are the different fastener categories. However, we will focus on screws. There are various types of screws available in the market. The screws have different head types and head styles. Therefore, we present this comprehensive screw size chart and thread count guide. It has helpful information that will enable you to understand the difference and get the actual screw sizes.  

Related: Cornhole Board Size and dimensions guide (for DIY)

Screw Size schart
Wood Screw Size schart

Screw Size Chart and Thread Count Guide

Screw SizeFractionsMillimeter and Inches
#11/16”1.58750 mm 0.0625 inches
#25/64”1.98437 mm 0.07812 inches
#33/32”2.38125 mm 0.09375 inches
#47/64”2.77812 mm 0.10937 inches
#51/8”3.17500 mm 0.125 inches
#69/64”3.57187 mm 0.14062 inches
#85/32”3.96875 mm 0.15625 inches
#911/64”4.36562 mm 0.17187 inches
#103/16”4.76250 mm 0.1875 inches
#1113/64”5.15937 mm 0.2031 inches
#127/32”5.55625 mm 0.21875 inches
#1315/64”5.95312 mm 0.2344 inches
#14¼”6.35000 mm 0.25 inches
#1617/64”6.74687 mm 0.2656 inches
#1819/64”7.54062 mm 0.29687 inches
#205/16”7.93750 mm 0.3125 inches
#243/8”9.52500 mm 0.375 inches

Screw Thread Count

¼ x 20¼ x 28
5/16 x 185/16 x 24
3/8 x 163/8 x 24
7/16 x 147/16 x 20
1/3 x 131/3 x 20
5/8 x 115/8 x 18
¾ x 103/8 x 16
7/8 x 97/8 x 14
1 x 81 x 14

The Different Types of Screws

The following are the four major types of screws available in the market.

1.  Wood Screws

These are designed for connecting items such as metals to wooden bases. Generally, wood expands and shrinks depending on the surrounding temperature. Therefore, you need a specialized screw that would be effective in a head wood screw drill. If you are a carpenter, you can use composite screws in addition to wood screws when using composite material.

Wood screws have the capability of bending before snapping. Therefore, they are not used to drill holes in metals.

2. Sheet Metal Screws

These screws are typically sturdier and stronger than wooden screws because they are made of steel. Steel is the most common material used for the manufacture of screws. These screws are used for applications in a variety of materials but not on metals because they strictly stay in place once screwed on.  Note that tapped holes are required before a machine screw such as a hex head screw is inserted.

The sheet metal screws are self-tapping, meaning they do not need pre-drilled holes into the source before inserting them. They are best for application in heavy gauge sheet metal.

3. Phillips Head Screw

Its flat screw head cannot be used on sheet metal cross head screws. If you are always working with screws, be sure to get yourself at least one of these types of screwdrivers. When using these screws, have a countersunk hole to ensure that the countersinking flat head screws are in place.

4. Drywall Screws

Most people have embraced the drywall screws as the standard fasteners to secure full or partial sheets of drywall on wood studs or on ceiling joists. Different types of such screws include coarse threads and finer thread drywall screws. Also, there are differences between their pitch sizes. The coarse threads have a large thread pitch and the finer threads have a smaller thread pitch. The drywall screws intended for construction always range from 1 inch to 8 inches long.  This is because building materials vary in thickness. You can be working with dense materials, heavy materials, or even soft materials.

Drywall screws installed in homes can be ½ -inch thick with the 5/8 thick drywall screws being used in garages and walls adjacent to furnace rooms. The ¼ inch thick drywall screws are used as facing for walls, ceilings or to form curves. For kitchen and bathrooms, use the ½ -inch thick screws.

Internal Hex Socket-Head Set Screw

These are socket set screws with a hexagonal head.

Screw Acronyms

The following information will be helpful to those who are starting out.

  • ST-Self-tapping; these screws do not require pre-drilled holes. Some are also referred to as thread cutter screws because they create threads in existing holes in metals with brittle They, therefore, save a lot of time.
  • TT-Twin thread: a screw is installed and removed faster than a single thread, making the thread more secure.
  • TFT-Twin Fine Thread: they are a little less coarse threads than the non-fine thread screws. They, therefore, soot into drilled holes easily.

Understanding Screw Sizes

It is not enough for you to understand the acronyms and quotations on the packaging. You need to be conversant with the screw sizes. This is because it sometimes gets tricky when it comes to sizing the screws, both metric sizes, and imperial sizes. Thread count also measures screw sizes. For example, a female ¼-20 socket screw has a diameter of ¼ and 20 female threads per inch.

Imperial and Metric Screw Sizes

Most of the companies combine both the imperial and metric sizes on the same box screws. However, when purchasing the screws online, you might find out that most retailers do not do this. Therefore, you are required to know the difference between the two sizes. Knowing the difference helps minimize the possibility of getting the wrong sizes.

Explanation on Imperial Screw Sizes

The screws used for wood application are available in two distinct sizes. The larger the number, the larger the diameter. Therefore, a size 12 screw is larger than a size 4. The screws from gauge 6 and above have twice the diameter’s head. Also, the given length for the screws is the length that is usually buried in the wood or in other materials. The head of the raised screw is usually not included. Therefore, the screw size is determined by the gauge and the length.

Explanation on Metric Screw Sizes

If you are unskilled, it would be difficult for you to understand the metric system. This is because you are not conversant with it or still working with imperial. The metric and imperial system uses the diameter sizes measured in millimeters instead of a gauge table. Coincidentally, the gauge is approximately the size of the screw head in millimeters. Therefore, a size 6 gauge screw has a head that is almost equal to 6 mm wide.

If you are a professional, you understand how difficult it is to effectively correlate the diameter of the metric, the gauge (imperial), and the head sizes. Therefore, it is important that you know there is no information that can guarantee a perfect correlation. This might be why most professionals prefer getting the screws personally to ensure they get the right screw sizes.

The imperial diameter (in 16th of an inch) of the screw head is usually twice the gauge (imperial). Use the formula below to calculate an estimate of the screw head and gauge. Gauge= (Head diameter in sixteenths of an inch X 2 ) – 2. E.g. 5/16 head times two equals 10, minus two equals 8. The Gauge is 8.

The above formula shows that the imperial gauge diameter in millimeters is almost half the gauge.  Most people do not know the said relationship. Therefore, having the formula in the screw size charts and thread count guide gives you an added advantage.

How to measure screw size?

How to Measure a Screw Size by wikiHow

Imperial & Metric Threads Sizes Chart

The thread sizes are given in nominal sizes, not actual measurements. For instance, a bolt size of 5.9 mm is referred to as a 6mm thread. Often, thread sizes in inches are specified by nominal thread major diameter and threads per inch. For example, for a screw size 10-24, the first digit (10) refers to the nominal thread major diameter. The second digit (24) refers to threads per inch. When the nominal thread diameter is smaller than ¼”, the value is indicated as #1or No. 1.

What Else You Should Know About Fasteners

Any manufacturing application requires that you use the correct fastener. To do this, youmust have the basic fastener concepts when being involved in FASTENER BUYING. You alsoneed to have driving torque requirements to help you tighten the fastener. You can get this information from any Fastener SuperStore near you. Read more about Fastener Basics and Type Charts

Screw size chart explained for wood screws (video)

Wood Screw Sizes Explained – A Beginners Guide by Training Hands Academy

Conclusion on understanding a screw size chart

Finding the right screw sizes can be a tedious task.  There are a dozen screw head types that work in a variety of applications. The screw size chart and thread count thread guide are the ultimate guides to your choice of the correct size of screws you require.

We hope the guide was helpful!! Feel free to leave a comment.

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