Machinery's Handbook, 31st Edition
2048 British Standard ISO Metric Screw Threads position, capital for nuts, lower case for bolts. If the two class designations for a thread are the same (one for the pitch diameter and one for the crest diameter), it is not necessary to repeat the symbols. As examples, a bolt thread designated M10-6g signifies a thread of 10 mm nominal diameter in the Coarse Thread Series having a tolerance class 6g for both pitch and major diameters. A designation M10 × 1-5g6g signifies a bolt thread of 10 mm nominal diameter having a pitch of 1 mm, a tolerance class 5g for pitch diameter, and a tolerance class 6g for major diameter. A designation M10-6H signifies a nut thread of 10 mm diameter in the Coarse Thread Series having a tolerance class 6H for both pitch and minor diameters.
Nut (Internal Thread)
In practice the root is rounded and cleared beyond a width of P /8
H /8
P /4
30 ° 30 °
Pitch line
5/8 H
P /8
H
H /4 H /4
P /2
P
90 °
Axis of nut
Bolt (External Thread)
P P /8
In practice the root is rounded and cleared beyond a width of P /8
H /8
P /2
3/8 H 30 °
5/8 H
Pitch line
H
H /4
P /8
P
90 °
Axis of bolt
Fig. 3. Maximum Material Profiles for Internal and External Threads A fit between mating parts is indicated by the nut thread tolerance class followed by the bolt thread tolerance class separated by an oblique stroke. Examples: M6-6H/6g and M20 × 2-6H/5g6g. For coated threads, the tolerances apply to the parts before coating, unless otherwise specified. After coating, the actual thread profile shall not at any point exceed the maximum material limits for either tolerance position H or h. Fundamental Deviation Formulas.— The formulas used to calculate the fundamental de - viations in Table 2 are: EI G = + (15 + 11 P ) EI H = 0 es e = − (50 + 11 P ) except for threads with P ≤ 0.45 mm es f = − (30 + 11 P ) es g = − (15 + 11 P ) es h = 0 In these formulas, EI and es are expressed in micrometers and P is in millimeters.
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