Tap-Fix Screws - for Aluminium or Zinc Die Casting and Steel and Aluminium Sheet Materials

This article provides Tap-Fix Hole size recommendations for metals using two common process scenarios; Die Cast and All ductile sheet materials.  

Tapfix screws are thread rolling screws with a trilobularTM shaped body that reduces friction during threadforming in the parent material. They have been designed to provide consistent torque performance, lower end load and lower thread forming torque.   

Industry common suggested thread engagement guidelines 

Powdered Metal or Cast Iron  50 - 65% 

Colled Rolled Steel  65 - 70% 

Aluminium  70 - 80% 

Thin Sheet Metals  80 - 95%  

 

Table 1: Suggested hole sizes for Aluminium or Zinc die casting.  

The minimum length of thread engagement should be equal to twice the diameter of the screw. The hole diameter should provide for 65% to 75% thread engagement to ensure optimum assembly performance.

Tap Fix Hole Geometry 1

 

Table 1
Metric Sizes
Screw Size Hole Diameter as Cast Std Taper F Hole Dia as Drilled L Length of thread eng't H Boss Dia. Min. J Distance to Edge
Top A Bottom B
Min Max Min Max
M2 x 0.40 1.91 1.83 1.81 1.73 1.81 4 3.32 1
M2.5 x 0.45 2.39 2.31 2.28 2.2 2.28 5 4.15 1.2
M3 x 0.50 2.9 2.82 2.76 2.68 2.76 6 4.98 1.3
M3.5 x 0.6 3.31 3.23 3.21 3.13 3.21 7 5.81 1.6
M4 x 0.7 3.82 3.74 3.64 3.56 3.64 8 6.64 1.8
M4.5 x 0.75 4.31 4.23 4.11 4.03 4.11 9 7.47 2
M5 x 0.8 4.8 4.72 4.58 4.5 4.58 10 8.3 2.1
M6 x 1.0 5.74 5.66 5.48 5.4 5.48 12 9.96 2.6
M6.3 x 1.0 6.05 5.97 5.78 5.7 5.78 13 10.46 2.6
M7 x 1.0 6.78 6.7 6.48 6.4 6.48 14 11.62 2.6
M8 x 1.25 7.69 7.61 7.35 7.27 7.35 16 13.28 3.3
M10 x 1.5 9.64 9.56 9.22 9.14 9.22 20 16.6 3.9
M12 x 1.75 11.59 11.51 11.09 11.01 11.09 24 19.92 4.6

 

Table 1
Inch Sizes
Screw Size Hole Diameter as Cast Std Taper F Hole Dia as Drilled L Length of thread eng't H Boss Dia. Min. J Distance to Edge
Top A Bottom B
Min Max Min Max
2-56 0.081 0.078 0.077 0.074 0.077 0.172 0.197 0.046
3-48 0.093 0.09 0.088 0.085 0.088 0.198 0.208 0.054
4-40 0.105 0.102 0.099 0.096 0.099 0.224 0.22 0.065
5-40 0.118 0.115 0.112 0.109 0.112 0.25 0.232 0.065
6-32 0.128 0.125 0.122 0.119 0.122 0.276 0.242 0.081
8-32 0.155 0.152 0.148 0.145 0.148 0.328 0.272 0.081
10-24 0.177 0.174 0.168 0.165 0.168 0.38 0.315 0.108
10-32 0.182 0.179 0.174 0.171 0.174 0.38 0.315 0.081
12-24 0.203 0.2 0.194 0.191 0.194 0.432 0.359 0.108
1/4-20 0.235 0.232 0.224 0.221 0.224 0.5 0.415 0.13
5/16-18 0.297 0.294 0.284 0.281 0.284 0.625 0.519 0.144
3/8-16 0.359 0.356 0.343 0.34 0.343 0.75 0.623 0.162
7/16-14 0.419 0.416 0.4 0.397 0.4 0.875 0.726 0.186
1/2-13 0.481 0.478 0.46 0.457 0.46 1 0.83 0.2

 

Table 2: Suggested Pilot hole sizes for Steel & Aluminium sheet materials 0.5mm through to 12mm.  

The following table illustrates suggested pilot holes for Steel (Rockwell B 55-75) and Aluminium (Rockwell B 40-70) will give satisfactory results in many cases.

Table 2
Suggested Pilot Hole Sizes
Material Steel Aluminium Steel Aluminium Steel Aluminium Steel Aluminium Steel Aluminium
Thickness 0.5 - 2mm 1.5 - 3.5mm 3 - 6.5mm 6 - 8mm 8 - 12mm
M2 x 0.4 1.75 1.7 1.8 1.75 - - - - - -
M2.5 x 0.45 2.25 2.2 2.3 2.25 2.35 2.3 - - - -
M3 x 0.5 2.7 2.6 2.75 2.7 2.8 2.75 - - - -
M3.5 x 0.6 3.1 3.1 3.2 3.1 3.2 3.2 3.25 3.2 3.3 3.25
M4 x 0.7 3.6 - 3.7 3.6 3.75 3.7 3.75 3.7 3.8 3.75
M5 x 0.8 - - 4.5 4.5 4.6 4.5 4.7 4.6 4.7 4.7
M6 x 1.0 - - 5.4 5.4 5.5 5.4 5.6 5.5 5.7 5.6
M8 x 1.25 - - 7.3 7.3 7.4 7.3 7.5 7.4 7.6 7.5
M10 x 1.5 - - - - 9.25 9.2 9.3 9.25 9.4 9.3
M12 x 1.75 - - - - - - 11.2 11.1 11.3 11.2

 



Note: Due to the fact that fastening applications differ greatly, the above information is for guidance only and is correct to the best of our knowledge. The customer must satisfy themselves with the performance of the fastener and validity of the data. TR Fastenings will not be held responsible for any failure that may occur from the use of this information.