Inch series bolting

NOTE 1. This section of this British Standard relates to inch series bolting for use with inch series pipe flanges, valves, and fittings as specified in British Standards such as BS 10, BS 1660 and BS 3293 and also for general purpose containing purposes.

Dimensional requirements are given for four designs of studbolts, three designs of alloy steel studs and associated nuts, which use ISO inch (Unified) screw threads in the following diameters (see figures 4 and 5):

Inch series bolts and screws (and associated nuts) may also be used for flange bolting and in such cases selection should be made from BS 1768 or BS 1769.

NOTE 2. BS 1768 specifies low and high tensile medium carbon and alloy steel hexagon bolts and nuts, BS 1769 specifies low tensile mild steel hexagon bolts and nuts (heavy series).

3.1 Studbolts

3.1.1 General

The forms of the studbolts shall comply with those shown in figure 4(a), (b), (c) or (d). Dimensions shall be as given in 3.1.2 to 3.1.8 and tables 16 to 19.

3.1.2 Nominal length

The tolerances on nominal length shall be as given in table 17.

NOTE 1. The preferred nominal lengths are given in table 18. If lengths other than these are requested (see appendix C) the increments of nominal length should be as follows:

(a) ¼ in for lengths up to and including 12 in;

(b) ½ in for lengths over 12 in.

NOTE 2. The length of stud is excluded from the nominal length (see 1.2.2.1).

3.1.3 Length of thread

For studbolts having plain portions as shown in figures 4(b), (c) and (d), the basic length of thread shall be equal to the nominal diameter plus 0.375 in.

For studbolts in figures 4(b) and 4(c), the limits on the length of thread shall be plus 2 pitches, minus 0.

3.1.4 Length of reduced diameter portion

The basic length of the reduced diameter portion shall be equal to 0.6 times the nominal diameter (see figure 4(d) and item (d) (5) of appendix C).

The following tolerances shall apply to this dimension:

(a) +0.030, -0 in for lengths up to and including 1.2 in;

(b) +0.060, -0 in for lengths over 1.2 in and up to and including 2.1 in.

3.1.5 Length of thread plus length of reduced diameter portion

The following tolerances shall apply to this dimension:

(a) ±0.030 in for lengths up to and including 2 in;

(b) ±0.060 in for lengths over 2 in and up to and including 6 in.

3.1.6 Ends

The ends of studbolts shall be finished with a point having an included angle of approximately 90° to a depth slightly exceeding the depth of thread. Nominal lengths of points for reference purposes shall be as given in table 19.

3.1.7 Diameter of plain portion

The diameter of the plain portion shall not exceed the maximum values given in table 16.

NOTE: The diameter of the reduced portion should be stated by the purchaser in the order (see appendix C). Under normal conditions a minimum of 0.95 times the minor thread diameter is used, but for studs subject to particularly onerous conditions (such as high temperature service) diameters less than this may be used.

Table 16. Diameter of plain portion, maximum and minimum sizes of studbolts: Inch series

3.1.8 Screw threads

Screw threads shall be ISO Unified inch coarse pitch series (UNC) for sizes up to and including 1 in diameter, and 8 threads/in (8 UN series) for sizes >1 in and above in accordance with BS 1580.

NOTE: The tolerance class should be stated by the purchaser in the order (see appendix C), but for most conditions the following are applicable:

(a) Class 2A (see BS 1580) for grades B7, L7, B7A and B16, B16A, B16B;

(b) class 2AG for other materials.

Table 17. Tolerance on nominal length of studbolts: Inch series

Table 18. Preferred nominal length of studbolts: inch series (based on flanges s specified in BS 1560: Section 3.1)

Table 19. Length of point (see 3.2.6) for studbolts: inch series

3.2 Studs

3.2.1 General

The forms of the studs shall comply with those in figure 5(a) or (b) or (c). Studs to figure 5(a) shall comply with BS 2693: Part 1, covering sizes up to 1½ in nominal diameter. Pitch details shall comply with 3.2.10.

The dimensions of studs to figure 5(b) shall be as given in 3.2.2 to 3.2.10 and tables 16, 17 and 19 for studbolts.

3.2.2 Nominal length

The nominal lengths shall be in the following increments:

• (a) increments of ⅛ in for lengths up to and including 5 in;
• (b) increments of ¼ in for lengths above 5 in.

NOTE. Nominal length excludes length of point (see 1.3.3.1).

The tolerances on nominal length shall be as given in table 17.

3.2.3 Length of metal end of thread

For studs to figure 5(b) the length of full form thread at the metal end shall be the nominal diameter except where high strength case studs are used with weak flange materials in which case the metal end threaded length shall be equal to 1.5 times the nominal diameter.

3.2.4 Length of nut end of thread

For studs as shown in figure 5(b) the basic length of thread shall be as given in table 20.

Table 20. Length of thread for studs: inch series

3.2.5 Length of reduced diameter portion

The basic length of the reduced diameter portion shall be 0.6 times the nominal diameter (see figure 5(b)), and shall be rounded up to the next 1/16 in.

The following tolerances shall apply to this dimension:

• (a) ±0.030,– in for lengths up to and including 1½ in;
• (b) ±0.060,– in for lengths over 1½ in.

3.2.6 Length of thread plus length of reduced diameter portion

The following tolerances shall apply to this dimension:

• (a) ±0.030 in for lengths up to and including 2 in;
• (b) ±0.060 in for lengths over 2 in and up to and including 6 in.

3.2.7 Ends

The nut ends shall be finished with a point having an included angle of approximately 90° to a depth slightly exceeding the depth of thread. Lengths of points shall be as given in table 19.

The metal ends shall be finished as follows:

• (a) For studs as illustrated in figure 5(b) the corner shall be broken at 45° to give a smooth edge;
• (b) For studs as illustrated in figure 5(c) the dimensions shall comply with the scale of sizes given in table 21.

Table 21. Stud dimensions: inch series

3.2.9 Diameter of reduced portion

The diameter of the reduced portion shall not exceed the maximum values given in table 16.

NOTE: The diameter of the reduced portion should be stated by the purchaser in the order (see appendices C). Under normal conditions a minimum of 0.65 times the minor reduced diameter is used, but for studs subject to particularly corrosive or severe environments (such as high temperature service) diameters less than this may be used.

3.2.10 Screw threads

Screw threads shall be ISO Unified inch coarse pitch series (UNC) for sizes up to and including 1 in diameter, and 8 thread/in (8 UN series) for sizes 1⅛ in and above, in accordance with BS 1580.

NOTE. The tolerance class (see BS 1580) should be stated by the purchaser in the order (see appendix C), but for most conditions the following are applicable:
(a) the metal end of studs should be to the tolerance class 2A for all materials;
(b) the run end of studs should be to the following tolerance classes:

• (1) class 2A for B7, L17, B7A and B16, B16A, B16B;
• (2) class 2AG for other materials.

3.2.11 Tolerances on nominal length

The tolerances on nominal length shall be as shown in table 17.

3.3 Nuts for use with inch series studbolts and studs

3.3.1 Dimensions

Nuts shall comply with the dimensions and tolerances given in table 22 or 23.

NOTE. Nuts of the following grades (see table 4) should be supplied as heavy series (see table 22) unless the purchaser requests the normal series: 2H    4    7    8C    8T

3.3.2 Faces

Heavy series nuts (see table 22) and normal series nuts (see table 23) shall have a chamfer of approximately 30° on the non-bearing face. The bearing face shall be finished with either a washer face or a chamfer of approximately 30°.

The bearing face shall be machined or have a surface finish equal to that produced by machining.

The faces of the nut shall be square to the axis of the thread of the nut within the tolerances given in tables 22 and 23 (see figures 6 and 7) when tested as described in appendix E.

3.3.3 Screw threads

Screw threads shall be ISO inch (UNC) for sizes up to and including 1 in diameter and 8 threads/in (8 UN series) for sizes 1⅛ in diameter and above in accordance with BS 1580 and shall conform to the tolerances for class 2B specified in that standard.

NOTE. See item (d) of appendix C.

The screw threads of nuts shall be concentric with the hexagon within a tolerance of F T213, FIM, using the width across the flats as the reference datum.

Table 22. Dimensions of heavy series nuts: inch series

Table 23. Dimensions of normal series nuts:inch series