British Association screw threads, or BA screw threads, are a set of small screw threads, the largest being 0BA at 6 mm diameter. They were, and to some extent still are, used for miniature instruments and modelling.
They are unusual in that they were probably the most "scientific" design of screw, starting with 0BA at 6.0 mm diameter and 1.0 mm pitch and progressing in a geometric sequence where each larger number was 0.9 times the pitch of the last size. They then rounded to 2 significant figures in metric and then converting to inches and rounding to the thousandth of an inch. This anticipated worldwide metrication by about a century. The design was first proposed by the British Association in 1884[1][2] with a thread angle and depth based on the Swiss Thury thread,[3] it was adopted by the Association in 1903.
The Thury thread was different in that it went both positive and negative all the way up to a size of −20 which was 75.2 mm diameter by 8.23 mm pitch (p). The Thury numbers were rounded to three significant figures. The Thury thread form had the crests rounded at 1/6p and the roots rounded at 1/5p so the thread angle was close to 47.5° but not exactly. This was simplified in the BA thread definition by defining the thread angle to be 47.5° exactly and the thread form to be symmetrical with a depth of 3/5p.
The British Standards Institution recommends the use of BA sizes in favour of the smaller British Standard Whitworth (BSW) and British Standard Fine (BSF) thread screws (those below 1⁄4inch).[4]: 4 Generally, the 0BA size was dropped in place of 7⁄32inch BSF in assemblies that included larger fasteners, however, in smaller equipment that was primarily electronic/electrical the 0BA size would typically be used in place of the BSF or BSW screw where it was the largest size required.
BA threads are still used in some precision instruments, such as optics and moving-coil meters, relays etc. A 2BA thread is used to connect the metal barrel of a dart to its shaft — as such, it is one of the few common uses of this thread in North America.
In the UK, 2BA threads are commonly found in the old imperial British Engineering Standards Association (BESA) conduit boxes, and 4BA threads in light switch and socket back boxes which are still in use (but not installed) today.
^"First Report of the BA Committee on small screws". sizes.com. Retrieved 2016-07-23.
^"Second Report of the British Association for the Advancement of Science's Small Screws Committee". sizes.com. 1884. Retrieved 2016-07-23.
^"Thury Thread". sizes.com. Retrieved 2016-07-23.
^Cite error: The named reference bs93:2008 was invoked but never defined (see the help page).
and 27 Related for: British Association screw threads information
ISO general-purpose metric screwthreads ("M" series threads) are defined in international standard ISO 68-1. Each thread is characterized by its major...
default handedness for screwthreads. Therefore, most threaded parts and fasteners have right-handed threads. Left-handed thread applications include:...
by the different thread angles of 60° and 55° respectively. BritishAssociation (BA) screwthreads, named after the BritishAssociation for Advancement...
a straight thread and the latter called a tapered thread. More screwthreads are produced each year than any other machine element. Threads are generally...
British Standard Fine (BSF) is a screwthread form, as a fine-pitch alternative to British Standard Whitworth (BSW) thread. It was used for steel bolts...
The small Edison screw has nine threads per inch, or a pitch of 1⁄9 in or 2.8222 mm per thread. The medium Edison screw has seven threads per inch, or a...
engineering, the thread angle of a screw is the included angle between the thread flanks, measured in a plane containing the thread axis. This is a defining...
diameter. In manufactured parts, holes with female screwthreads are often needed; they accept male screws to facilitate the building and fastening of a finished...
sublineages of the SARS-CoV-2 Omicron variant BritishAssociationscrewthreads, a set of small screwthreads Ba F.C., a Fijian football club Ba game, a...
Sellers originally developed the USS thread, and set forth many of its details in his paper, "A System of ScrewThreads and Nuts", presented in April 1864...
single thread step interrupted screw cannot be inserted where any threads of the breech lay in the radial vector as any threads of the screw. Thread lock...
Taps and dies are tools used to create screwthreads, which is called threading. Many are cutting tools; others are forming tools. A tap is used to cut...
At a minimum, a screw drive is a set of shaped cavities and protrusions on the screw head that allows torque to be applied to it. Usually, it also involves...
sockets BS 92 Screwthreads, British Standard Whitworth and their tolerances BS 93 Specification for BritishAssociation (B.A.) screwthreads with tolerances...
early "screw" mechanisms for sealing the breech consisted of threaded blocks which were screwed tightly into the breech after loading, but the threads themselves...
An ice screw is a threaded tubular screw used as a running belay or anchor by climbers on steep ice surface such as steep waterfall ice or alpine ice...
philanthropist. In 1841, he devised the British Standard Whitworth system, which created an accepted standard for screwthreads. Whitworth also created the Whitworth...
committee was set up to put into practice the system of British Associationscrewthreads, which had been settled on but not implemented in 1884. More broadly...
valve body. The threaded section of the stem goes through a hole with matching threads in the bonnet. Globe valves may have a screw-in, union, or bolted...
the first industrially practical screw-cutting lathe in 1800, which allowed for the standardisation of screwthread sizes for the first time. Maudslay's...
usually fastened in non-threaded ways (such as clinching or upsetting against a washer). Maudslay standardized the screwthreads used in his workshop and...
leakproof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. A screw-in bonnet is the simplest, offering a durable, pressure-tight...
Global Information