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What is an A F spanner?

Author

John Castro

Published Mar 18, 2026

What is an A F spanner?

Width across flats is the distance between two parallel surfaces on the head of a screw or bolt, or a nut, mostly for torque transmission by positive locking. The term width across flats (AF) is used for the following forms: 2-socket = round material with two surfaces. 4-socket = profile square section.

Also question is, what does AF mean in spanners?

Width across flats is the distance between two parallel surfaces on the head of a screw or bolt, or a nut, mostly for torque transmission by positive locking. The term width across flats (AF) is used for the following forms: 2-socket = round material with two surfaces. 4-socket = profile square section.

One may also ask, what is the difference between AF and SAE spanners? AF does mean "across flats" these are the same size as SAE sizes. Whitworth tools are stamped with the fractional size,followed by a W , as previously mentioned and the fractional size does mean the thread diameter as opposed to head size with SAE sizes. A 9/16"W socket is the same size as a 1" SAE socket.

Secondly, what is the difference between AF and Whitworth spanners?

AF was introduced much later and refers to Across Flats and was related to UNC(universal national coarse) and UNF(universal national fine) threads in the USA A 1/2 inch Whitworth socket is for a nut that fits on a 1/2 inch diameter thread, and is usually 1.5 times the diameter of the screwed rod across the flats of the

What does AF mean in measurements?

AF is a means of measuring the size of the hexagonal heads of imperial sized bolts and nuts for the purpose of indicating the size spanner to use. It has been around for more than my 55 years. It means "Across the Flats".

What is the difference between AF and Imperial?

Imperial are another range of sizes completely;tend to be found on older UK vehicles. Most people take imperial to be inch sizes which are AF. If you're thinking of Whitworth then you'll struggle to get a whit set for cheap money these days. Most AF sizes are useful for when the metric nut is rounded etc.

Is BSF the same as SAE?

These bolts have a fine thread, with a different thread count from an American National Fine (also known as SAE). The BSF threads have an included angle as the Whitworth threads, with an included angle of 55° where as the American National Fine (SAE) threads have an included angle of 60°.

What is bigger than a 1/2 inch socket?

Society of Automotive Engineers (SAE) measurement

3/8 in, 7/16 in, 1/2 in, 9/16 in, 5/8 in, 11/16 in, 3/4 in, 13/16 in, 7/8 in, 15/16 in, 1 in, 1-1/16 in, 1-1/8 in, 1-3/16 in, 1-1/4 in.

Is Whitworth the same as Imperial?

British Standard Whitworth (BSW) is an imperial-unit-based screw thread standard, devised and specified by Joseph Whitworth in 1841 and later adopted as a British Standard.

What spanner size is M8?

13mm

What does AF mean on Imperial tools?

The most common Imperial standard in classics built after 1960 is the 'increments of one inch across flats' or 'AF' system. A good quality AF socket set will fit the vast majority of fittings on a British classic car.

What does AF mean on tools?

Width across flats is the distance between two parallel surfaces on the head of a screw or bolt, or a nut, mostly for torque transmission by positive locking. The term width across flats (AF) is used for the following forms: 2-socket = round material with two surfaces.

What is the difference between SAE and Whitworth?

These are both machine thread (and hex) standards based on fractional inch diameters. Whitworth is rarely used any more, while SAE is still in use, though metric hardware has become more common in most industries. Thread counts are different, hex sizes (nuts and bolt heads) are different sizes.

What size is a 9/16 spanner?

Imperial and Metric Spanner Sizes
BOLT DIAMETER (INCHES)AF SPANNER SIZE (INCHES)SPANNER SIZE (MM)
3/8 INCH9.52 MM
1/4 INCH7/16 INCH11.11 MM
5/16 INCH1/2 INCH12.7 MM
3/8 INCH9/16 INCH14.29 MM

Is Whitworth the same as UNF?

Whitworth heads are NOT the same size as the equivalent UNC/UNF - they are larger. For this reason, it is imperative that a set of Whitworth wrenches are purchased before working on any antique British machinery. Otherwise, expect rounded-off heads and busted knuckles, trademarks of the careless craftsman.

Is af the same as UNF?

In simple terms AF iis the size of spanner used on bolts / nuts with UNC and UNF threads. AF meaans acroos flats and is the imperial size of the head. Both UNC and UNF (Unified National Coarse / Fine) use AF heads.

Is UNF same as BSF?

BSF and BSW are Britisch measurement systems, while UNF and UNC are American measurement systems. BSF and UNF are the fine thread systems, while BSW and UNC are the coarse thread systems.

How do spanner sizes work?

Modern spanner sizes refer to the distance across the flats of the hexagonal nut or bolt they would fit. A 17mm spanner therefore fits a nut 17mm across its flats and this is normally a nut to fit a 10mm diameter bolt (M10).

What is equivalent to a 27mm socket?

Wrench Size And Conversion Table
InchesMillimetersSpanner
1.02426mm26mm
1.06327mm1 1/16 AF; 27mm
1.1005/16 Wworth; 11/16 BSF
1.1251 1/8 AF

How many spanner sizes are there?

Metric Spanner Sizes
Nominal SizeSpanner Size
M1017mm
M1219mm
M1422mm
M1624MM

What does AF mean on a socket?

AF can stand for American Fractional; another term used for imperial. However, when applied to metric sockets, AF means 'Across Flats'. This means a 19mm AF socket will fit a nut or bolt head that measures 19mm across its flats.

What size is 7 32 in MM?

SAE to Metric Conversion Chart
SAEMetricInch
5mm0.197
5.5mm0.216
7/32"0.219
6mm0.236

How do you determine the spanner size of a bolt?

If the bolt size is up to M14,
  1. Spanner size =(Bolt size*1.5)+1.
  2. Eg. If Bolt size is M8, Then spanner size is (8*1.5)+1 =13.
  3. If bolt size is above M14,
  4. Spanner size = (Bolr size *1.5)
  5. Eg. If bolt size is M16, Then spanner size is (16*1.5) = 24.

What is 2ba in MM?

BA size chart
Screw NumbersDiameter of Screw Over ThreadSize
3 BA0.1610 inchNumber drill 29 3.4 mm 0.1339 inch
2 BA0.1850 inchNumber drill 22 4 mm 0.1575 inch
1 BA0.2090 inchNumber drill 16 4.5 mm 0.1772 inch
0 BA0.2360 inchNumber drill 9 5.1 mm 0.2008 inch

What size is 3/16 in MM?

Conversion table inches to mm
Dimensions — Inches to Metric
0.188”3/16”4.78 mm
0.250”1/4”6.35 mm
0.313”5/16”7.95 mm
0.375”3/8”9.53 mm

What size is smaller than a 13 16?

Metric / Standard Wrench Conversion Chart
Bolt DiameterMetricStandard
1/2"19mm3/4"
9/16"21mm13/16"
22mm7/8"
5/8"24mm15/16"

What is Whitworth size?

A Whitworth wrench is sized according to the diameter of the shank of the bolt, not the head. A 1/4 W (Whitworth) wrench is actually a bit larger than a 1/2″ American wrench—0.525″ to 0.500″. As if that wasn't enough, in 1924 it was decided that the heads of the Whitworth bolts were too large, so they were down-sized.

Is a F Imperial?

Both are considered Imperial,as well as a couple of others. Id be happily corrected on this. Yes, you are correct, A/F means 'across the flats' as opposed to the old Whitworth & BSW standards which were based on a proportion of the thread diameter (BSW being the smaller proportion of the 2).

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