Machinery's Handbook, 31st Edition
Metric Machine Screws 1797 Table 6. Recommended Nominal Screw Lengths for Metric Machine Screws Nominal Screw Length Nominal Screw Size M2 M2.5 M3 M3.5 M4 M5 M6 M8 M10 M12 2.5 PH 3 A PH 4 A A PH 5 A A A PH PH 6 A A A A A PH 8 A A A A A A A 10 A A A A A A A A 13 A A A A A A A A A 16 A A A A A A A A A H 20 A A A A A A A A A H 25 A A A A A A A A H 30 A A A A A A A H 35 A A A A A A H 40 A A A A A H 45 A A A A H 50 A A A A H 55 A A A H 60 A A A H 65 A A H 70 A A H 80 A A H 90 A H All dimensions in millimeters. 1 The nominal screw lengths included between the heavy lines are recommended for the respective screw sizes and screw head styles as designated by the symbols. A—Signifies screws of all head styles covered in this standard. P—Signifies pan head screws. H—Signifies hex and hex flange head screws.
Table 7. Clearance Holes for Metric Machine Screws ANSI/ASME B18.6.7M-1999 (Withdrawn), Appendix
Basic Clearance Hole Diameter a
Nominal Screw Size
Close Clearance b
Normal Clearance (Preferred) b
Loose Clearance b
M2 M2.5 M3 M3.5
2.20 2.70 3.20 3.70 4.30 5.30 6.40 8.40
2.40 2.90 3.40 3.90 4.50 5.50 6.60 9.00
2.60 3.10 3.60 4.20 4.80 5.80 7.00 10.00 12.00
M4 M5 M6 M8
M10 M12
10.50 13.00
11.00 13.50
14.50 a The values given in this table are minimum limits. The recommended plus tolerances are as follows: for clearance hole diameters over 1.70 to and including 5.80 mm, plus 0.12, 0.20, and 0.30 mm for close, normal, and loose clearances, respectively; for clearance hole diameters over 5.80 to 14.50 mm, plus 0.18, 0.30, and 0.45 mm for close, normal, and loose clearances, respectively. b Normal clearance hole sizes are preferred. Close clearance hole sizes are for situations such as critical alignment of assembled components, wall thickness, or other limitations which necessitate the use of a minimal hole. Countersinking or counterboring at the fastener entry side may be necessary for the proper seating of the head. Loose clearance hole sizes are for applications where maximum adjustment capability between the components being assembled is necessary. All dimensions in millimeters.
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