Machinery's Handbook, 31st Edition
Metric Screws and Bolts 1725 of other materials, and all materials for hex lag bolts, have properties as agreed upon by the purchaser and the manufacturer. Except for socket head cap screws, metric screws and bolts are furnished with a natural (as processed) finish, unplated or uncoated unless otherwise specified. Alloy steel socket head cap screws are furnished with an oiled black oxide coating (ther mal or chemical) unless a protective plating or coating is specified by the purchaser. Metric Screw and Bolt Identification Symbols.— Screws and bolts are identified on the top of the head by property class symbols and manufacturer’s identification symbol. Metric Screw and Bolt Designation.— Metric screws and bolts with the exception of socket head cap screws are designated by the following data, preferably in the sequence shown: product name, nominal diameter and thread pitch (except for hex lag screws), nominal length, steel property class or material identification, and protective coating, if required. Example: Hex cap screw, M10 × 1.5 × 50, class 9.8, zinc plated Heavy hex structural bolt, M24 × 3 × 80, ASTM A490M Hex lag screw, 6 × 35, silicon bronze. Socket head cap screws (metric series) are designated by the following data in the order shown: ANSI Standard number, nominal size, thread pitch, nominal screw length, name of product (may be abbreviated SHCS), material and property class (alloy steel screws are supplied to property class 12.9 as specified in ASTM A574M: corrosion-resistant steel screws are specified to the property class and material requirements in ASTM F837M), and protective finish, if required. Example: B18.3.1M—6 × 1 × 20 Hexagon Socket Head Cap Screw, Alloy Steel B18.3.1M—10 × 1.5 × 40 SHCS, Alloy Steel Zinc Plated. Metric Screw and Bolt Thread Lengths.— The length of thread on metric screws and bolts (except for metric lag screws) is controlled by the grip gaging length, L g max. This is the distance measured parallel to the axis of the screw or bolt, from under the head bearing surface to the face of a noncounterbored or noncountersunk standard GO thread ring gage assembled by hand as far as the thread will permit. The maximum grip gaging length, as calculated and rounded to one decimal place, is equal to the nominal screw length, L , minus the basic thread length, B , or in the case of socket head cap screws, minus the minimum thread length L T . B and L T are reference dimensions intended for calculation purposes only and will be found in Table 13 and Table 15 , respectively. Table 14. Basic Thread Lengths for Metric Round Head Square Neck Bolts ANSI/ASME B18.5.2.2M-1982 (R2010) Nom. Bolt Dia., D and Thread Pitch Bolt Length, L Nom. Bolt Dia., D and Thread Pitch Bolt Length, L ≤ 125 > 125 and ≤ 200 > 200 ≤ 125 > 125 and ≤ 200 > 200 Basic Thread Length, B Basic Thread length, B M5 × 0.8 16 22 35 M14 × 2 34 40 53 M6 × 1 18 24 37 M16 × 2 38 44 57 M8 × 1.25 22 28 41 M20 × 2.5 46 52 65 M10 × 1.5 26 32 45 M24 × 3 54 60 73 M12 × 1.75 30 36 49 … … … … All dimensions are in millimeters Basic thread length B is a reference dimension intended for calculation purposes only.
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