Metric Self-Threading Screws Machinery's Handbook, 31st Edition
1857
Table 11. Approximate Hole Sizes for Steel Types BF and BT Metric Thread Cutting Tapping Screws for Cast Metals and Plastics Nominal Screw Size and Thread Pitch Material Thickness Hole Size Drill Size a Nominal Screw Size and Thread Pitch Material Thickness Hole Size
Drill Size a
In Die-Cast Zinc and Aluminum
1.52 2.11 2.77 3.18 3.56 2.77 3.18 3.56 4.78 6.35 3.18 3.56 4.78 6.35 7.92 9.52 3.18 3.56 4.78 6.35 7.92 9.52 3.18 3.56 4.78
1.85 1.85 1.93 1.93 1.93 2.49 2.54 2.54 2.54 2.59 4.22 4.22 4.22 4.32 4.37 4.37 4.85 4.85 4.85 4.98 4.98 4.98 5.61 5.61 5.61
49 49 48 48 48 40 39 39 39 38 19 19 19 18 … … 11 11 11
3.18 3.56 4.78 6.35 7.92 3.18 3.56 4.78 6.35 7.92 6.35 7.92 9.52 3.18 3.56 4.78 6.35 7.92 9.52 3.18 3.56 4.78 6.35 7.92 9.52
3.05 3.05 3.05 3.18 3.18 3.78 3.78 3.78 3.86 3.86 5.79 5.79 5.79 7.14 7.14 7.14 7.14 7.37 7.37 8.74 8.74 8.74 8.74 8.84 8.84
31 31 31 … … 25 25 25 24 24
2.2 × 0.8
3.5 × 1.3
2.9 × 1
4.2 × 1.4
1 1 1
6.3 × 1.8
4.8 × 1.6
K K K K L L
8 × 2.1
5.5 × 1.8
9 9 9 2 2 2
… … … …
9.5 × 2.1
S S
6.3 × 1.8
Depth of Penetration
Nominal Screw Size and Thread Pitch
Hole Size 1.98 2.64 3.18 3.73 4.32 4.93 5.79 1.93 2.54 3.05 3.66 4.22 4.80 5.61
Drill Size a
Min.
Max.
In Phenol Formaldehyde
… 37 … 26 18 10 48 39 31 27 19 12 1
2.39 3.18 4.78 6.35 7.92 9.52 9.52 2.39 3.18 4.78 6.35 7.92 9.52 9.52
6.35 7.92 9.52 12.70 15.88 15.88 19.05 6.35 7.92 9.52 12.70 15.88 15.88
2.2 × 0.8 2.9 × 1.0 3.5 × 1.3 4.2 × 1.4 4.8 × 1.6 5.5 × 1.8 6.3 × 1.8 2.2 × 0.8 2.9 × 1.0 3.5 × 1.3 4.2 × 1.4 4.8 × 1.6 5.5 × 1.8 6.3 × 1.8
In Cellulose Acetate and Nitrate, Acrylic and Styrene Resins
2 19.05 a Customary drill size references have been retained where the metric hole sizes are direct conversions of their decimal inch equivalents. All dimensions are in millimeters except drill sizes. The finish (plating or coating) on metric tapping screws and the material composition and hardness of the mating component are factors that affect assembly torques in individ ual applications. Although the recommended installation hole sizes given in Table 7 through Table 9 were based on the use of plain unfinished carbon steel metric tapping screws, experience has shown that the specified holes are also suitable for screws having most types of commercial finishes. However, owing to various finishes providing different degrees of lubricity, some adjustment of installation torques may be necessary to suit indi vidual applications. Also, where exceptionally heavy finishes are involved or screws are to be assembled into materials of higher hardness, some deviation from the specified hole sizes may be required to provide optimum assembly. The necessity and extent of such deviations can best be determined by experiment in the particular assembly environment.
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