THREAD FORMING SCREWS 
Also known as thread rolling screws, thread forming screws are tapping screws that form their mating internal thread by displacing material adjacent to the hole and pushing it outwards into the open spaces between the threads of the screw. Thread forming screws are best used in fairly thin sections of malleable materials, such as plastic or wood. Unlike thread cutting screws, thread forming screws do not contain cutting slots and do not produce chips.
Because frictional resistance to driving is lower than for many alternative parts, thread forming screws offer better control of driving and tightening torques, and joint strength and integrity are often better.
Hole Sizes for Thread Forming Screws
|
Suggested Hole Sizes for Thread Forming Screws
Nominal
Screw Size |
Hole Diameter
|
Closest Drill Size to Mean Hole Diameter |
|||
Max |
Mean |
Min |
Drill size |
Drill Dia |
|
2 - 56 |
0.078 |
0.076 |
0.074 |
48 |
0.076 |
2 - 64 |
0.077 |
||||
3 - 48 |
0.090 |
0.087 |
0.084 |
44 |
0.086 |
3 - 56 |
0.089 |
||||
4 - 40 |
0.100 |
0.097 |
0.094 |
41 |
0.096 |
4 - 48 |
0.100 |
||||
5 - 40 |
0.113 |
0.110 |
0.107 |
35 |
0.110 |
5 - 44 |
0.112 |
||||
6 - 32 |
0.123 |
0.119 |
0.115 |
31 |
0.120 |
6 - 40 |
0.124 |
||||
8 - 32 |
0.150 |
0.146 |
0.141 |
20 |
0.147 |
8 - 36 |
0.148 |
||||
10 - 24 |
0.170 |
0.165 |
0.160 |
19 |
0.166 |
10 - 32 |
0.177 |
0.172 |
0.167 |
11-64 |
0.1719 |
12 - 24 |
0.198 |
0.192 |
0.186 |
11 |
0.191 |
12 - 28 |
0.196 |
||||
1/4 - 20 |
0.228 |
0.221 |
0.214 |
2 |
0.221 |
1/4 - 28 |
0.230 |
||||
5/16 - 18 |
0.289 |
0.218 |
0.273 |
K |
0.281 |
5/16 - 24 |
0.290 |
||||
3/8 - 16 |
0.349 |
0.339 |
0.329 |
R |
0.339 |
3/8 - 24 |
0.353 |
||||
7/16 - 14 |
0.409 |
0.397 |
0.385 |
X |
0.397 |
7/16 - 20 |
0.411 |
||||
1/2 - 13 |
0.471 |
0.457 |
0.443 |
29/64 |
0.4531 |
1/2 - 20 |
0.475 |
||||
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