What is the ideal hole size and thread engagement for tapping?

Designing the correct hole size when preparing for tapping is important. Holes that are too large may cause the tap to strip out or fail. If the hole is too small, it will cause the tap to bind, create excessive heat, wear, and could result in a broken tap trying to cut too much material. So we have a helpful chart for you to reference when choosing your hole and tap sizes.

The percentage of thread engagement in your design should also be intentional. If not designed for correctly, too little or too much thread engagement could weaken your parts, cause distortion in the material, or damage your hardware. Though it’s dependent on the intended use and overall design, soft materials such as Aluminum, Brass, Copper, and plastics work best with more thread engagement (75% of thread). Hard materials, such as steel, benefit from less engagement (50-70% of thread).

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We proudly use hardware by PEM

Flush Standoff, 4-40, .250" Zinc plus Clear Chromate

Aluminum: 5052, 6061, 7075 Steel: Mild, G30

SKUSO-440-8
Thread Size4-40 x .250″
Hole size in sheet (+0.003/-.0.000).168″
Minimum sheet thickness0.040″
Maximum sheet thickness.125″
Fastener materialSteel
Minimum distance hole C/L to edge0.230″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole..345″
Recommended panel materialSteel/Aluminum
Coating typeZinc
Length.250″
Aluminum material ranges (5052, 6061, 7075)0.040″-0.125″
Steel material ranges (CRS, HRPO, HR)0.048″-0.119″

We proudly use hardware by PEM

Flush Standoff, 4-40, .250" Passivated

Stainless Steel: 304, 316

SKUSO4-440-8
Thread Size440
Hole size in sheet (+0.003/-.0.000).166″
Minimum sheet thickness0.04″
Maximum sheet thickness.125″
Fastener material400 Stainless Steel
Minimum distance hole C/L to edge0.230″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole. Example shown with x2 of the same hardware..345″
Recommended panel materialStainless Steel
Coating typePassivated
Length.250″
304 Stainless Steel material ranges0.048″-0.125″
316 Stainless Steel material ranges0.060″-0.125″