If the thread is to be chased after galvanizing by heating and wire brushing, it is best to either leave the thread as-is, or over-tap the thread by 0.003 inches in diameter. This cleaning method will remove nearly all of the galvanized coating. This is the most common method for handling threads, especially when a threaded stud is welded onto a fabricated assembly.
Another method is to over-tap the thread before galvanizing, and then re-tap to the correct size after galvanizing. This will provide the most corrosion resistant product possible. Please follow this table for over-tapping dimensions.
|
Nominal Thread Size and Pitch (inches) |
Diametrical Allowance (inches) |
|
0.250 – 20 |
0.016 |
|
0.312 – 18 |
0.017 |
|
0.375 – 16 |
0.017 |
|
0.437 – 14 |
0.018 |
|
0.500 – 13 |
0.018 |
|
0.562 – 12 |
0.020 |
|
0.625 – 11 |
0.020 |
|
0.750 – 10 |
0.020 |
|
0.875 – 9 |
0.022 |
|
1.000 – 8 |
0.024 |
|
1.125 – 8 |
0.024 |
|
1.125 – 7 |
0.024 |
|
1.250 – 8 |
0.024 |
|
1.250 – 7 |
0.024 |
|
1.375 – 8 |
0.027 |
|
1.375 – 6 |
0.027 |
|
1.500 – 8 |
0.027 |
|
1.500 – 6 |
0.027 |
|
1.750 – 5 |
0.050 |
|
2.000 – 4.5 |
0.050 |
