螺纹前打孔数据
      
        
            
        	
				
            
            
              
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- 螺纹前打孔螺纹尺寸	钻头直径     下孔径       最小直径	 最大直径
3 × 0.5           2.5	2.59 (75%)     	2.459	2.599
4 × 0.7	3.3	3.39 (80%)	3.242	3.422
5 × 0.8	4.2	4.31 (80%)	4.134	4.334
6 × 1.0	5	5.13 (80%)	4.917	5.153
8 × 1.25          6.8	6.85 (85%)	6.647	6.912
10 × 1.5          8.5	8.62 (85%)	8.376	8.676
12 × 1.7          10.3	10.40 (85%)	  10.106	10.441
14 × 2.0          12	12.2  (85%)	11.835	12.210
16 × 2.0          14	14.2  (85%)	13.835	14.210
18 × 2.5          15.5	15.7  (85%)	15.294	15.744
20 × 2.5          17.5	17.7  (85%)	17.294	17.744
22 × 2.5          19.5	19.2  (85%)	19.294	19.744
24×3.0          21	       21.2(85%)    20.752	  21.252...