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Plastic and Sheet Metal 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!
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Table of Contents

Setup and Cost

Tapping your parts adds a $9 minimum to your cart total.

Save up to 70% or more with quantity discounts! We calculate quantity discounts based on several factors including material, operation type, number of operations on each part and number of duplicate parts. Our app will automatically provide quantity discounts based on your order.

Check out our processing page for information about typical lead times for tapping and other services.

Understanding Thread Types And Sizes for Fasteners

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)

 

Understanding 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.

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

Tap Size and Placement Considerations

At SendCutSend we automatically resize holes to perfectly fit the tap you need! That being said you’ll still want to reference our hole size chart when calculating the minimum distance required from other cut features. 

We’ll need the center of any tapped holes to be at least the following distance from other cut features: tap hole size/2 + the minimum tap hole-to-edge distance for the chosen material.

The minimum hole-to-edge distance is measured from the edge of the tapped hole to the nearest cut feature, and the specification can be found on each individual material info page by stock thickness. 

Below is a chart of SendCutSend’s available tap sizes. Each tap size is paired with the required through-hole size that will be needed in your design. 

Use the formula above to make sure there’s sufficient distance between tapped holes and other cut features to ensure optimal performance for your applications.

Thread/Tap Hole Size Chart

TapHole Size
MM
4-400.091″2.32
6-320.116″3.00
8-320.138″3.51
10-320.164″4.17
1/4-200.209″5.31
1/4-280.221″5.62
5/16-180.266″6.76
5/16-240.278″7.07
3/8-160.323″8.21
3/8-240.341″8.67
1/2-130.435″11.05
1/2-200.459″11.66
M2 x 0.40.065″1.66
M2.5 x 0.450.083″2.11
M3 x 0.50.102″2.60
M4 x 0.70.134″3.41
M5 x 0.80.170″4.32
M6 x 1.00.203″5.16
M8 x 1.250.274″6.96
M10 x 1.50.344″8.74

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.

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
  • 0.118″-0.220″ Polycarbonate
  • 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
  • For bent parts, place tapped holes at least 1/2 the full die width away from the bend line to avoid distortion. You can find the die width used to form our bendable materials on each individual material info page. Check out our bending guidelines for more information.
  •  
  • Tapping only available perpendicular to the main surface
  • Minimum 1″ x 1.5″ part size for tapping
  • Maximum 36″ x 46″ 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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