Tapping Guidelines

So you’ve designed something fantastic (or maybe you’re about to) that requires some tapping. Cool. We can’t wait to help you make it a reality. Here are some essential guidelines to help us get it to you even faster!

Table of Contents

Setup and Cost

Tapping your parts adds $29 to your order, per unique design. We’ll include up to 9 tapped holes for no additional charge. Pricing starts at $3 per tapping operation once you’ve met the minimum charge. See our handy chart below for examples.

# of Tapped Holes
Total Cost The Math
1 $29 $3 per hole x 1 = $3. $29 minimum used
5 $29 $3 per hole  x 5 = $15. $29 minimum used
10 $30 $3 per hole x 10 = $30 total
20 $60 $3 per hole x 20 = $60 total

For the best pricing over 50 tapped holes, please request a custom quote.

*Allow for an additional 2-5 business days (100 pieces or more may require additional time)

 

Understanding Thread Types And Sizes for Fasteners

 

Diameter

Diameter is simply a line of measurement crossing directly through the middle of your geometry, which, in this case, is your hole to be tapped and the fastener to be used.

Thread Engagement

Thread engagement is essentially just a fancy way of saying, “what percentage of threads on this bolt are engaged (or joined properly) with the threads on this nut?” It works the same for tapped holes and their appropriate fasteners. What’s important here is knowing your materials.

To make sure your parts have the required strength for your applications, you must be sure to take note of factors like tension and shear.

Thread Pitch

Thread pitch is a measurement depicting how many threads are in a given space. There are a few different ways to represent thread pitch:

  • SAE (Society of Automotive Engineers)
  • Metric
  • ANSI (American National Standards Institute)

SAE is represented by this format: ½-20. This measurement is read as a half-inch diameter with 20 threads per inch of the tapped length.

Metric is represented by this format: M10-1.25. This measurement is read as a 10mm diameter with 1.25mm between each thread. So, rather than counting threads per inch, the metric system directly measures the distance between two threads in mm. 

ANSI  is a unique beast and has its own standardized sizes that read like this: 10-24. These, like the other two systems, just reflect a particular standardized fastener size. If you need one of these, you likely already know, and if you aren’t sure, there are charts to verify dimensions in detail.

Coarse Thread vs. Fine Thread

You also need to understand the difference between coarse and fine threads concerning your project. 

Fasteners/holes with coarse threads have larger pitches compared to fine threads. This just means there are fewer threads per fastener/hole. In contrast, fine threads tend to have smaller pitches and, therefore, more threads. Easy enough, yeah? 

In most cases, you’ll likely be using coarse threads, but there are some scenarios in which the use of a fine thread hole/fastener would be preferable. 

If you’re considering whether or not to use a fine thread tap, consider these pros and cons, but understand that this is not an exhaustive list: 

Pros of Fine Thread

  • Stronger than coarse thread size-for-size
  • They allow for finer adjustment in some applications
  • Less tendency to loosen

Cons of Fine Thread

  • More prone to seizing and galling
  • Less suitable to high-speed assembly due to seizing
  • Need longer thread engagements

Choosing the Correct Hole Size

Referencing a standard Tap/Drill chart will be necessary while you’re designing your taps. Using the correct hole size is extremely 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.

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).

Below is a chart of SendCutSend’s available thread options. Each tap size will be paired with the required drill (through-hole) size that will be needed on your design. So be sure to check and double-check your measurements.

Thread Option Chart

Tap Drill Size 75% MM Drill Size 50% MM
4-40 0.089 2.26 0.096 2.44
6-32 0.107 2.71 0.116 2.95
8-32 0.136 3.45 0.144 3.66
10-32 0.159 4.04 0.170 4.32
1/4-20 0.201 5.11 0.219 5.56
1/4-28 0.213 5.41 0.228 5.79
5/16-18 0.257 6.53 0.277 7.04
5/16-24 0.272 6.91 0.281 7.14
3/8-16 0.313 7.94 0.332 8.43
3/8-24 0.332 8.43 0.348 8.84
1/2-13 0.422 10.72 0.453 11.51
1/2-20 0.453 11.51 0.469 11.91
M2 x 0.4 0.063 1.60 0.069 1.75
M2.5 x 0.45 0.081 2.05 0.087 2.20
M3 x 0.5 0.098 2.50 0.106 2.70
M4 x 0.7 0.130 3.30 0.138 3.50
M5 x 0.8 0.165 4.20 0.177 4.50
M6 x 1.0 0.197 5.00 0.213 5.40
M8 x 1.25 0.268 6.80 0.283 7.20
M10 x 1.5 0.335 8.50 0.354 9.00

Choosing the Correct Tap for Your Material Thickness

Ideally, you want as much thread engagement/depth of thread as possible. Depending on the application, you may be able to get away with much less. For the best strength, you should try to aim for 1-1.5X the bolt diameter to depth ratio.

For example, an 8-32 bolt should have roughly (0.136”-204”) thread/material depth.

Tap Min thickness
(2 threads of engagement)

Max thickness/depth

4-40 0.050 0.300
6-32 0.063 0.400
8-32 0.063 0.400
10-32 0.063 0.600
1/4-20 0.100 0.650
1/4-28 0.071 0.650
5/16-18 0.111 0.650
5/16-24 0.083 0.650
3/8-16 0.125 1.000
3/8-24 0.083 1.000
1/2-13 0.154 1.200
1/2-20 0.100 1.200
9/16-18 0.111 1.200
5/8-18 0.111 1.200
M2 x 0.4 0.031 0.200
M2.5 x 0.45 0.035 0.200
M3 x 0.5 0.039 0.300
M4 x 0.7 0.055 0.400
M5 x 0.8 0.063 0.600
M6 x 1.0 0.055 0.650
M8 x 1.25 0.098 0.650
M10 x 1.5 0.118 1.000
M12 x 1.75 0.138 1.200

Materials Available for Tapping

  • 0.063”-0.500” 5052/6061/7075 Aluminum
  • 0.063”-0.250” Copper
  • 0.063”-0.250” Brass
  • 0.060”-0.500” 304 Stainless Steel
  • 0.059”-0.500” Mild Steel
  • 0.050”-0.250” 4130 Chromoly
  • 0.125”-0.250” Delrin
  • 0.250”-0.500” HDPE
  • 0.125”-0.250” ABS

Quick File Setup & Design Points

  • Size holes to the correct drill size for the given tap using our chart
  • Keep tapped holes minimum .500” from any bend lines
  • Do not have duplicate circles or tap symbols in your design
  • Tapping only available perpendicular to the main surface
  • Minimum 1.5 x 1.5″ part size for tapping

What to Expect On Finished Parts

  • Parts may have some light oil residue
  • They may require some deburring
  • Tapped holes near bends could distort and may need chasing

Closing Statement

We hope this guide helps you design your parts for greater success with us, and we ask that you take the time to check out the other guidelines pages to make sure everything looks great. In the end, it will save us all a tremendous amount of time and energy!

If you have specific questions regarding your design and they aren’t covered in our guidelines, don’t hesitate to reach out to support@sendcutsend.com. Our friendly and talented folks will get back to you as soon as possible!

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