What is the Diameter of a 4 40 Screw? (2023)

Interestingly, there was a time when the market had just two options, either a slotted or Philips one.

Choose any one as per your need, pick a specific length, and simply relax after that.

However, the fastener market of today is quite diverse because it wants to offer DIY plenty of options for the same.

Technically, we have two kinds of diameters on the screws, viz. the minor and the major diameter, and they also help in naming the screws by giving them numerical codes.

What Is the Diameter of A 4 40 Screw?

0.1120 or 14/125 – Major Diameter.

Threads per inch, TPI – 40

Determining the screw size and TC:

Thread count has two other names like thread pitch or the threads per inch, TPI.

These calculations help us to be a step ahead and make sure that our bolt and screw go head-to-head.

For instance, if you have a ¼ 20 screw, it simply means that it has a major diameter of ¼ inch and has 20 as its thread count or TPI.

  • Allow the screw to rest on a flat surface, and its top is free towards the surface edge because we need its threads to rest flat.
  • Now take a steel rule and place it on the screw axis and remember to count the first thread as zero.
  • Begin to count the thread gaps that are occurring for each inch of the screw and divide those by their length.
  • For instance, if there are five gaps for each unit of length, we get the thread count as 1/5 = 0.2 inches.
  • Now place this on the flat surface and lay down the steel ruler between two threads to measure the diameter.

PS– Kindly measure from the outermost ends first and do not measure if the threads are in a worn-out condition.

Technical definitions of some important terms related to a screw:

Pitch diameter– It has another name which is the effective diameter.

If we imagine a co-axial cylinder intersecting the thread surface such that the point of intercept on this cylinder meets the flanks of the thread’s groove, that diameter is pitch dia.

Major and Minor diameter– If we imagine the same co-axial cylinder that touches the crest of another thread/ root of the internal thread, this length is the major diameter.

If it touches the root only or crest of the internal part, then it is the minor diameter.

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(Video) How to Read a Metric Screw Thread Callout

Root– The groove’s bottom.

Flanks– Straight sides which connect to its bottom and root.

PS– Choosing the right screw size is equally important. First of all, you should look at whether you need to apply a screw indoors or outdoor.

Because for indoor purposes, we can use the less expensive zinc-coated versions of screws which are a lot less cheap yet visibly appealing, and for outside, go for a little costly alternative.

Some of the best options for outside use can be Stainless steel or silicon bronze.

Some recommended items:

01. #4-40 x 1/2″ Button Head Socket Cap Screws – $5.67 to $9.80

  • ½ inches and other five sizes available.
  • Full thread and Allen socket with stainless steel make.
  • A bright finish with twenty-five pieces from bridge fasteners.
  • Hex drive and rust-free with 18-8 stainless steel built and long-lasting make.

02. SNUG Fasteners 100 Qty #6 x 3/4″ – $0.06/ single

  • Zinc coated Philips’s wood screws.
  • Hundred counts!
  • A fine deep thread type.
  • Carbon steels make and 4 x 6 x 0.5 inches dimensions.
  • Multi-use is available.

Some other questions,

Related Questions and Frequently Asked Questions (FAQ):

Q1.) What does screw #4-40 mean?

Answer:It simply means 40 threads/ inch.

14/125 dia.

These are the standard ways of naming these machine screws with their diameter and TPI/ threads per inch.

Q2.) What is the diameter of the #4 screw?

Answer:0.1120 inches.

These are the taken from the standard but major diameters of Industry table.

They go from #0 to #16 where #0 has a diameter of 0.0600, and #16 has a diameter of 3/8 inches.

Q3.) What is the difference between an M3 and 4-40?

Answer: Not much!

We already know that the #4 screw has a diameter of about 0.112 inches as per the original formula, and for drilling, the closest size is 1/8″.

On the other hand, the closest relative to this #4-40 sizing is the M3 which is a machine screw and in metric units is almost the same.

Q4.) What is the pitch for a 4 40 thread?

Answer:It must be 0.635.

(Video) Wood Screw Sizes Explained - A Beginners Guide

Pitch is the distance among the screw grooves and is different from lead. We use the pitch with inch method of screw sizing.

Similarly, a #6-32 with 32 Threads per inch will have a pitch of 0.794.

Q5.) What is the most accurate way of measuring the diameters of screws and bolts?

Answer:We begin to measure the diameter, also called the major diameter of a screw, by calculating its total distance from the outer thread to another outer thread.

READ: Modified Bitumen vs. Roll Roofing

In other words, an outer thread of one side to a similar one on its other outer side.

This is the actual size of the screw.

Q6.) How can one judge which screw size they need?


Use a very common thumb rule that the given screw should be entering at least 50% into the given material.

For instance, for a 2 x 4 material, A ¾” is the best fit because it will follow the rule above.

Another factor is checking their diameter and gauge.

Q7.) What are the diameter of an M3 and that of an M3.5?

Answer:3.0mm is the Nominal diameter for an M3 where its pitch is 0.5.

On the other hand, the M3.5 has a diameter of 3.5 and 0.6 as its pitch.

PS – These are ISO Machine Metric ST dimensions.

Q8.) Does 4-40 follow the UNC or UNF?


In metric – M3 x 0.5.

In UNC – 4-40.

(Video) How to Measure a Screw Size

And, In UNF – 4-48.

PS – UNC means Unified National Coarse Thread which is comparable to the ISO metric thread version.

And UNF – Unified national fine thread.

Q9.) What are screw sizes?

Answer:They are numerical nomenclatures of diameters and their corresponding length if screw.

They are measured in inches.

The smallest diameter is zero, and the largest can exceed 24.

However, the most usable of these are from sizes four to twelve, and even in them, the most popular are six, eight, and ten.

Q10.) Are the #12 screw and 1 4 the same?

Answer:Yes, just a minor difference.

#12 screw is just ¼ inch short of the second one.

Q11.) What is the accurate drill size or clearance hole DS for #4-40 fasteners?

Answer:0.1120 units.

For 5-40, the same becomes 0.125 inches.

Q12.) What do you mean by the major diameter of a given thread in scientific terms?

Answer:Let there be an imaginary co-axial cylinder that is just able to touch the crest of an external thread.

Or it touches the root of an internal one; this is the major diameter of the thread.

Q13.) What is the pitch diameter of a screw?

Answer:it is that diameter wherein the thickness of thread becomes equal to its corresponding space between them.

READ: What Are Golden Corral Lunch Hours?

And if the flats are the same as well on its top and bottom, we say that this pitch diameter will coincide with the sloping side and towards the middle of the thread.

(Video) SHOP TIPS #381 Understanding Machine Screw Sizes tubalcain

Q14.) How to compare screws?

Answer:In other words, how to determine its size and TC?

  • Lay down the screen on a smooth flat surface.
  • Then, keep a steel rule towards the axis of the screw.
  • You must count how many thread gaps are coming per inch of the screw.
  • Lastly, divide its gaps to the length and place them on a flatter surface.
  • Simply measure with the steel ruler.

Q15.) What is the actual size for a 2 x 2 screw?

Answer:1.5″ x 1.5″ is their actual denominations.

So, you must take a shorter screw concerning that distance + the board thickness like ½” or ¾.”

Q16.) What is the diameter of a #8 screw?


This is the major diameter, and it has eight threads per inch with a length of 1-1/4″.

This is if we measure it from tip to tip.

Final Verdict:

Screws and fasteners have grown in numbers and complexities and can be numerically named if we know their major diameter and length.

Thread per inch TPI is a crucial number to know as well and helps in naming the screw.

Screws must be purchased by thinking whether you need them for indoor usage or outdoor usage.

An indoor usage does not need fancy screws, and one can buy a less expensive version like zinc-coated carbon steel one and more for their visual looks.

While, for usage on the outside, you need more on the features like a corrosion-free built than other visual appeals.

For this reason, use silicon or stainless-steel screws for their long-term sturdiness.

The next issue can be to choose the right size of screw and length, and for this, we have an easy-to-use thumb rule.

The rule suggests that the screw must enter around 50% inside the bottom material or penetrate this much thickness.

Another factor can be the diameter and gauge of the screw, where gauges come from #2 to #16.

Only choose #12 to #16 if you are working on an extremely difficult material that is super thick or similar woodworks.

(Video) Picking the Right Drill Bit Size for a Screw

#6, 8, and #10 are okay for most indoor DIY works and are the best choices.

Thanks For Reading!



What is the diameter of 4-40 screw? ›

External Thread Screw Threads Size Chart
Screw SizeClass ThreadMajor Diameter
56 more rows

What is the diameter of a #4-40 thread? ›

0.1245'' Diameter, 0.1250'' Length, 4-40 Thread, Stainless Steel Black.

What is the diameter of a 4-40 machine screw head? ›

Product Images
Product details
Dimensional standardASME B18.6.3
Diameter in inches0.112"
Head height0.070" - 0.080"
Head diameter0.205" - 0.219"
14 more rows

What does screw size 4-40 mean? ›

The first number refers to the size (and therefore strength) of the screw shaft; the second to the pitch (number of threads per inch) on the screw. So a #4-40 screw has 40 threads per inch, a 1/4-20 has 20 threads per inch. A #4 screw is a smaller diameter (and therefore weaker) than a #6.

What size is 4-40 in MM? ›

UNC Thread ANSI/ASME B1. 1
Nominal DiameterMajor Diameter InchMajor Diameter mm
#4 - 40 UNC0.1122.845
#5 - 40 UNC0.1253.175
#6 - 32 UNC0.1383.505
#8 - 32 UNC0.1644.166
31 more rows

What is a 4-40 screw in metric? ›

Fastener Conversion Chart
Inch EquivalentMetric Size-PitchISO and IFI Rec.
4- 404- 48M3x .5
6- 326- 40M3.5x .6
8- 328- 36M4x .7
10- 2410- 32M5x .8
13 more rows

What is the minor diameter of a 4-40 thread? ›

Fastener and Screw Design, Formula Calculations
Screw SizeClass ThreadMinor Diameter
76 more rows

What size is 4-40 threaded rod? ›

316 Stainless Steel Fully Threaded Rod, #4-40 Thread Size, 12" Length, Right Hand Threads.

What size drill for a 4-40? ›

Tap Drill Size Chart
Bolt SizeDrill SizeDecimal (in)
4-40 NC#430.089
4-48 NF#420.094
1/8-40 NS#380.102
90 more rows

What is the diameter of a #4 screw? ›

American Screw Sizes
SizeNearest FractionInch
8 more rows
May 25, 2022

What are 4 40 screws used for? ›

Diameter - Thread Pitch: #4-40

Commonly used for: Drawer Slides. Machinery.

What is the head diameter of a #4 screw? ›

Screw Gauge Guide
Screw GaugeHead diameter (mm)Shank diameter (mm)
28 more rows

How many mm is a size 4 screw? ›

Metric versus Imperial equivalent screw dimensions.
Diameter (mm)Length (mm)Length (in)
4702 3/4
5301 1/4
5401 1/2
27 more rows

How thick is a #4 screw? ›

US Screw size conversion chart:
Screw SizeInch DecimalNearest Fraction
#20.086 in.3/32"
#30.099 in.7/64"
#40.112 in.7/64"
#50.125 in.1/8"
7 more rows

What are 4 screws used for? ›

The following are among the most common standard screw sizes: #4 screw: These small screws are just 7/64 inches in diameter and available in lengths ranging from ⅜ inch to ¾ inch. They're used for things like small crafts and light-duty hinges.

What does 4 40 UNC mean? ›

Metal screws tend to have more threads per inch than wood screws, for instance. Coarse screws also have a larger pitch measurement than fine screws. A #4-40 UNC-3A x . 5 screw has 40 threads per inch. A ¼-20 screw, by comparison, only has 20 threads.

What diameter is 4 mm? ›

4mm = 5/32 inch (= a bit over 1/8 inch) 5mm = just over 3/16 inch.

What are the dimensions of a 4 40 nut? ›

Product Images
Product details
Thread count40
Diameter in inches0.112"
Width across the flats1/4" (Min 0.241", Max 0.250")
9 more rows

Is 4 40 the same as M3? ›

The closest size screw in metric to a #4-40 machine screw is M3.

What does 4 M4 screw mean? ›

Metric screw sizes vs standard

Standard metric screw dimensions are determined by the pitch and the major diameter, which as the illustration shows, is the largest diameter of the screw. Let's say it's 4mm, in which case it appears as M4 (the M means metric).

What diameter is a 4 40 rod? ›

Heavy duty steel and nickel plated. Includes screws and hex nuts. For use with . 093 diameter (4-40) threaded rods.

What is major diameter of a screw? ›

The major diameter or outside diameter is the diameter over the crests of the thread, measured at right angles to the thread axis.

How big is a 40mm screw? ›

Imperial to metric screw conversion chart
Screw GaugeDiameter (inches)Diameter (mm)
27 more rows
Jul 15, 2022

What measurement is 40 rods? ›

Etymologically rod is also akin to the Dutch rood which referred to a land area of 40 square rods, equal to one-quarter acre, or 10,890 square feet (1,012 square metres). It also denoted just one square rod, or 272.25 square feet (25.29 square metres).

What is the thread size of a 4 an fitting? ›

AN SizeMetal Tube O.D.Thread Size
-4 AN1/4"7/16" - 20 SAE
-5 AN5/16"1/2" - 20 SAE
-6 AN3/8"9/16" - 18 SAE
-8 AN1/2"3/4" - 16 SAE
5 more rows

What size is H4 screw? ›

【SIZE】H4 hex head, 1/4-inch hex shank, 2.56-inch (65mm) total long.

What is the minor diameter of a 4 40 thread? ›

Fastener and Screw Design, Formula Calculations
Screw SizeClass ThreadMinor Diameter
76 more rows


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