BRITISH STANDARD THREADS Machinery's Handbook, 31st Edition
2115
British Association (BA) Standard Thread, Basic Dimensions BS 93:1951 (obsolescent)
Bolt and Nut Effective Diameter, mm
Designa tion Number
Threads per Inch (approx.)
Depth of Thread, mm
Major Diameter, mm
Radius, mm 0.1808 0.1627 0.1465 0.1320 0.1193 0.1067 0.0958 0.0868 0.0778 0.0705 0.0633 0.0561 0.0506 0.0452 0.0416 0.0380 0.0344
Pitch, mm 1.0000 0.9000 0.8100 0.7300 0.6600 0.5900 0.5300 0.4800 0.4300 0.3900 0.3500 0.3100 0.2800 0.2500 0.2300 0.2100 0.1900
Minor Diameter, mm
0 1 2 3 4 5 6 7 8 9
0.600 0.540 0.485 0.440 0.395 0.355 0.320 0.290 0.260 0.235 0.210 0.185 0.170 0.150 0.140 0.125
6.00 5.30 4.70 4.10 3.60 3.20 2.80 2.50 2.20 1.90 1.70 1.50 1.30 1.20 1.00 0.90
5.400 4.760 4.215 3.660 3.205 2.845 2.480 2.210 1.940 1.665 1.490 1.315 1.130 1.050 0.860 0.775
4.80 4.22 3.73 3.22 2.81 2.49 2.16 1.92 1.68 1.43 1.28 1.13 0.96 0.90 0.72 0.65
25.4 28.2 31.4 34.8 38.5 43.0 47.9 52.9 59.1 65.1 72.6 82.0 90.7
10 11 12 13 14 15 16
102 110 121
0.115 134 Tolerances and Allowances: Two classes of bolts and one for nuts are provided: Close Class bolts are intended for precision parts subject to stress, no allowance being provided between maximum bolt and minimum nut sizes. Normal Class bolts are intended for gen eral commercial production and general engineering use; for sizes 0 to 10 BA, an allow ance of 0.025 mm is provided. Tolerance Formulas for British Association (BA) Screw Threads 0.79 0.675 0.56
Tolerance (+ for nuts, − for bolts)
Class or Fit
Major Dia.
Effective Dia.
Minor Dia.
0.15 p mm 0.08 p + 0.02 mm 0.16 p + 0.04 mm 0.20 p mm 0.10 p + 0.025 mm 0.20 p + 0.05 mm 0.25 p mm 0.10 p + 0.025 mm 0.20 p + 0.05 mm
Close Class 0 to 10 BA incl. Normal Class 0 to 10 BA incl. Normal Class 11 to 16 BA incl.
Bolts
Nuts All Classes
0.12 p + 0.03 mm
0.375 p mm
In these formulas, p = pitch in millimeters. Instrument Makers’ Screw Thread System.— The standard screw system of the Royal Microscopical Society of London, also known as the “Society Thread,” is employed for microscope objectives and the nose pieces of the microscope into which these objectives screw. The form of the thread is the standard Whitworth form. The number of threads per inch is 36. There is one size only. The maximum pitch diameter of the objective is 0.7804 inch and the minimum pitch diameter of the nose-piece is 0.7822 inch. The dimensions are as follows: Male thread outside dia. max., 0.7982 inch min., 0.7952 inch root dia. max., 0.7626 inch min., 0.7596 inch Female thread root of thread max,. 0.7674 inch min., 0.7644 inch top of thread max., 0.8030 inch min., 0.8000 inch The Royal Photographic Society Standard Screw Thread ranges from 1-inch diameter upward. For screws less than 1 inch, the Microscopical Society Standard is used. The Brit ish Association thread is another thread system employed on instruments abroad. American Microscope Objective Thread (AMO).— The standard, ANSI/ASME B1.11- 1958 (R2016), describes the American microscope objective thread, AMO, the screw thread form used for mounting a microscope objective assembly to the body or lens turret
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online