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Home Fastener Guides Measuring Screws
screw measurements diagram

(T) Thread Diameter. Also called major diameter.

(S) Shank Diameter

(R) Root Diameter. Also called minor diameter.

Screw Size Fractions Decimals Millimeter
#1 1/16" 0.0625" 1.58750
#2 5/64" 0.078125" 1.98437
#3 3/32" 0.09375" 2.38125
#4 7/64" 0.109375" 2.77812
#5 1/8" 0.125" 3.17500
#6 9/64" 0.140625" 3.57187
#8 5/32" 0.15625" 3.96875
#9 11/64" 0.171875" 4.36562
#10 3/16" 0.1875" 4.76350
#11 13/64" 0.203125" 5.15937
#12 7/32" 0.21875" 5.55625
#13 15/64" 0.234378" 5.95312
#14 1/4" 0.250" 6.35000
#16 17/64" 0.265626" 6.74687
#18 19/64" 0.296875" 7.54062
#20 5/16" 0.3125" 7.93750
#24 3/8" 0.375" 9.52500

Efficient Measurement of Screws and Bolts

There are different ways to identify screws and bolts namely by diameter, length, and thread pitch. The measurement of length is done from the head to the tip of the thread. To get the correct hardware or fastener for the work, it is important to find the diameter and length of the fastener. Different kinds of fasteners like hex, pan, button, socket cap, and round head screws are measured from the head to the tip of the threads.

The measured fastener features are STANDARD, DIAMETER, THREAD PITCH, SHANK LENGTH, HEAD, and THREAD LENGTH. It is very simple to measure the fasteners as there are different to correctly measure it. The fastener cannot be measured with a ruler and you can get here the right idea about the measure of fasteners before buying.

How are the diameters of screws and bolts measured?

The measurement rule of major diameter – The distance from the outer thread from a particular side to the other.

The measure rule of minor diameter – The distance from the bottom thread cavity from a particular side to the other.

The nominal measurement is done by allotting a common number for sizes for 1/4" or lower. For the perfect, it is important to measure the length of the screw and bolt. Without a correct measurement, you will always end up with too long or short fasteners.

Here is the list of number and their decimal equivalent:-


The Length of Screws and Bolts

The length of screws and bolts are the distances from their head to the tip or blunt end of the product. All screw types are either flat on the top or bottom.


Mostly the screws are flat on the bottom of the head and these are measured from the head to the tip.


Countersunk screws are flat on the top of the head and it is measured from the top to the tip.


The hex and hex washer head screws are flat on the top and the bottom. But the measure is done from the bottom of the head to the tip.


The oval headed screws have some exceptions in its measurement. The measurement starts from the widest point of the head to the tip.


The drilling screws are measured from the bottom of the head to the tipping point.

Do you need more details on the fasteners and its measurement? Contact us on 1-949-551-0770 / 949-415-0005 to have a discussion with the experts. We are committed to providing you the accurate information for the effectiveness of fasteners in your work.