This listing is for a pack of 20 brass machine screws size 12BA, length 1/8 inch, slotted cheese head.

Unused re-packaged old stock.

Uncoated brass, but the screws in the pack may vary in colour from brass to black.

UK shipping is the same for any number of packets. Overseas shipping is set at £10 but we can check and issue more accurate rates on request.

BA (British Association) screws were proposed in the 19th century by the British Association for the Advancement of Arts and Sciences, based on a Swiss standard. The sizes start at 0BA, which has a diameter of 6mm and a thread pitch of 1mm (the same as M6 6mm coarse metric thread) with a thread angle of 47.5 degrees (unlike Whitworth which uses 55 deg, or ISO which is 60 deg). Successive numbered sizes have a thread pitch 0.9 times that of the previous size, and the outside diameter of the thread is 6 x (pitch)^1.2. The resulting figures were converted to inch measurements, and rounded off, but the following are the sizes in millimetres:

Notation pitch diameter comment

0BA        1.00    6.00          base

1BA        0.90    5.30

2BA        0.81    4.70          about 3/16"

3BA        0.73    4.10

4BA        0.66    3.60

5BA        0.59    3.20          about 1/8"

6BA        0.53    2.80

7BA        0.48    2.50

8BA        0.43    2.20

9BA        0.39    1.90

10BA      0.35    1.70          about 1/16"

12BA      0.28    1.30

 BA size fasteners became universal throughout the sphere of British influence around the world until superseded by metric sizes in the 1980s. Typical applications include electrical equipment, precision instruments, tooling, toys, clocks, models, and aircraft and vehicle components, for any threaded fastener smaller than 1/4in. They are still useful for vintage item repairs and restoration of all the above, and are commonly used in making new items in the original style in model engineering.