British Standard Fine Thread Chart

Introduction:

The British Standard Fine (BSF) thread chart is a comprehensive guide to a widely used thread system in the United Kingdom and other countries following British engineering standards. Threaded fasteners are fundamental components in various industries, and understanding the BSF thread chart is crucial for engineers, manufacturers, and DIY enthusiasts alike. This article aims to provide an overview of the BSF thread system, its characteristics, applications, and the benefits it offers in specific scenarios.

THREAD DATA CHART:
British Thread (British Standard Fine)—Fine Pitch
Nominal Size BSF	Thread Form Type	Major Diameter mm d=D	Pitch mm p	Threads per inch tpi	Pitch Diameter mm d2=D2	Minor Diameter Male Thd. d3	Thread Height H1	Tap Drill Diameter mm
3/16″	BSF	4.763	0.794	32	4.255	3.747	0.508	4.00
7/32″	BSF	5.556	0.907	28	4.975	4.394	0.581	4.60
1/4″	BSF	6.350	0.977	26	5.725	5.100	0.625	5.30
9/32″	BSF	7.142	0.977	26	6.518	5.893	0.625	6.10
5/16″	BSF	7.938	1.156	22	7.199	6.459	0.739	6.80
3/8″	BSF	9.525	1.27	20	8.712	7.899	0.813	8.30
7/16″	BSF	11.113	1.411	18	10.209	9.304	0.904	9.70
1/2″	BSF	12.700	1.588	16	11.684	10.668	1.017	11.10
9/16″	BSF	14.288	1.588	16	13.272	12.256	1.017	12.70
5/8″	BSF	15.875	1.814	14	14.712	13.549	1.162	14.00
11/16″	BSF	17.463	1.814	14	16.300	15.137	1.162	15.50
3/4″	BSF	19.050	2.117	12	17.693	16.336	1.355	16.75
13/16″	BSF	20.638	2.117	12	19.281	17.924	1.355	18.25
7/8″	BSF	22.225	2.309	11	20.747	19.269	1.479	19.75
1″	BSF	25.400	2.54	10	23.774	22.148	1.627	22.75
1-1/8″	BSF	28.575	2.822	9	26.769	24.963	1.807	26.50
1-1/4″	BSF	31.750	2.822	9	29.944	28.138	1.807	28.75
1-3/8″	BSF	34.925	3.175	8	32.893	30.861	2.033	31.50
1-1/2″	BSF	38.100	3.175	8	36.068	34.036	2.033	34.50
1-5/8″	BSF	41.275	3.175	8	39.243	37.211	2.033	38.00
1-3/4″	BSF	44.450	3.629	7	42.126	39.802	2.324	40.50
2″	BSF	50.800	3.629	7	48.476	46.152	2.324	47.00
2-1/4″	BSF	57.150	4.234	6	54.440	51.730	2.711	53.00
2-1/2″	BSF	63.500	4.234	6	60.790	58.080	2.711	59.00
2-3/4″	BSF	69.850	4.234	6	67.140	64.430	2.711	n/a
3″	BSF	76.200	5.08	5	72.946	69.692	3.253	n/a
3-1/4″	BSF	82.550	5.08	5	79.296	76.042	3.253	n/a
3-1/2″	BSF	88.900	5.645	4 1/2	85.285	81.670	3.614	n/a
3-3/4″	BSF	95.250	5.645	4 1/2	91.635	88.020	3.614	n/a
4″	BSF	101.600	5.645	4 1/2	97.985	94.370	3.614	n/a
4-1/4″	BSF	107.950	6.35	4	103.886	99.822	4.066	n/a

What is the British Standard Fine (BSF) Thread?

The British Standard Fine thread is a type of thread specification commonly employed in the UK for a range of fasteners, including bolts, screws, and nuts. It is based on the Whitworth thread form and features a finer pitch compared to the British Standard Whitworth (BSW) thread. The fine pitch enhances thread engagement, providing better resistance against loosening due to vibrations and a more secure fastening solution.

BSF Thread Characteristics:

The BSF thread system is characterized by the following parameters:

a. Thread Pitch: The distance between adjacent thread crests on the fastener is finer in BSF threads than in BSW threads. This results in a higher number of threads per inch.

b. Angle: The thread angle in BSF threads is the same as in BSW threads, which is 55 degrees.

c. Thread Depth: The thread depth of the BSF threads is shallower compared to the BSW threads.

Applications of BSF Threads:

The British Standard Fine thread finds application in various industries and scenarios, including:

a. Automotive Industry: BSF threads were historically popular in the automotive industry, especially in classic cars and motorcycles. However, with the advent of metric threads, their use has diminished, but they are still encountered in vintage vehicle restoration and maintenance.

b. Aerospace: In some aircraft components and aviation-related applications, BSF threads are used due to their ability to handle high loads and offer secure fastening.

c. Industrial Machinery: Certain precision machinery, hand tools, and equipment utilize BSF threads to ensure robust and reliable connections.

d. Antique Restoration: When restoring antiques and vintage items, the original BSF threads might need replacement or repair using compatible BSF fasteners.

Advantages of BSF Threads:

a. Strength: The fine pitch in BSF threads provides increased strength and resistance to vibrations, making them suitable for heavy-duty applications.

b. Precision: The finer thread pitch allows for more precise adjustments and tighter tolerances, critical in applications where accuracy is paramount.

c. Historical Relevance: BSF threads hold historical significance, and their use is essential for preserving the authenticity and structural integrity of vintage machinery and equipment.

Conclusion:

The British Standard Fine Thread Chart is a valuable resource for engineers, mechanics, and enthusiasts involved in various industries. Understanding the specifications, applications, and benefits of BSF threads allows for informed decision-making when selecting fasteners for specific projects. While the use of metric threads has become more widespread, the historical significance and unique advantages of BSF threads ensure their relevance in select applications, particularly in restoring and maintaining vintage machinery and vehicles.