Machinery's Handbook, 31st Edition
1742 Clearance Holes Metric Fasteners.— The recommended drill and hole sizes for metric fasteners are tabu lated in Table 2a . The minimum recommended hole is the drill size and the maximum recommended hole size is based on standard tolerances. The hole sizes for metric fasten - ers are in agreement with ISO 273, Fasteners-Clearance Holes for Bolts and Screws , except that ISO 273 covers fastener sizes M1 through M150. Table 2a. Clearance Holes for Metric Fasteners ANSI/ASME B18.2.8-1999 (R2017)
Normal
Close
Loose
Hole Diameter
Hole Diameter
Hole Diameter
Nominal Drill Size
Nominal Drill Size
Nominal Drill Size
Nominal Screw Size
Min.
Max.
Min.
Max.
Min.
Max.
M1.6
1.8 2.4 2.9 3.4 4.5 5.5 6.6
1.8 1.94 2.4 2.54 2.9 3.04 3.4 3.58 4.5 4.68 5.5 5.68 6.6 6.82
1.7 2.2 2.7 3.2 4.3 5.3 6.4 8.4
1.7 1.8 2.2 2.3 2.7 2.8 3.2 3.32 4.3 4.42 5.3 5.42 6.4 6.55
2
2
2.25
M2
2.6 3.1 3.6 4.8 5.8
2.6 2.85 3.1 3.4 3.6 3.9 4.8 5.1 5.8 6.1
M2.5
M3 M4 M5 M6
7
7
7.36 10.36 12.43
M8 M10 M12 M14 M16 M20 M24 M30 M36 M42 M48 M56 M64 M72 M80 M90
9
9
9.22
8.4 8.55 10 10.5 10.68 12
10 12
11
11
11.27 10.5
13.5 15.5 17.5
13.5 13.77 13 15.5 15.77 15 17.5 17.77 17
13 15 17 21 25 31 37 43 50 58 66 74 82 93
13.18 14.5 15.18 16.5 17.18 18.5 21.21 24 25.21 28 31.25 35 37.25 42 43.25 48 50.25 56
14.5 14.93 16.5 16.93 18.5 19.02
22 26 33 39 45 52 62 70 78 86 96
22 26 33 39 45 52 62 70 78 86 96
22.33 21 26.33 25 33.39 31 39.39 37 45.39 43 52.46 50 62.46 58 70.46 66 78.46 74 86.54 82 96.54 93
24 28 35 42 48 56 66 74 82 91
24.52 28.52 35.62 42.62 48.62 56.74 66.74 74.74 82.87 91.87
58.3 66.3 74.3
66 74 82
82.35 91 93.35 101
101 101.87 112 112.87
M100
107
107 107.54 104
104 104.35 112
Table 2b. Metric Clearance Hole Allowances
Fit Classes
Fit Classes
Nominal Screw Size
Nominal Screw Size M20, M24
Normal
Close
Loose
Normal
Close
Loose
M1.6
0.2 0.4 0.4 0.4 0.5 0.6
0.1 0.1 0.1 0.2 0.3 0.4 0.4 0.5
0.25 0.3 0.3 0.6 0.8
2 3 3 4 6 6 6 7
1 1 1 2 2 2 3 4
4 5 6 8
M2
M30
M2.5
M36, M42
M3
M48
M4, M5
M56-M72
10 11 11 12
M6 M8
1 2 2
M80 M90 M100
1 1
M10
M12-M16
1.5
1
2.5
… … … …
Dimensions are in millimeters. Recommended Substitute Drills.— If the clearance hole application is dimensioned in metric drill sizes for inch fasteners, or inch drill sizes for metric fasteners, Table 3a and Table 3b list the nearest standard drill size translations for the designated drills of Table 1a and Table 2a.
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