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Countersinking Design Guidelines

Following these guidelines will make designing for countersinking easy, and will ensure that your order is machined accurately and quickly.
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Table of Contents

Countersinking Setup and Cost

Countersinking adds a $9 minimum to your order.  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.

Part Sizing

The success of countersinking is heavily dependent upon the material thickness and the size of the part, so we’ve implemented sizing minimums and maximums your part will need to adhere to in order to be countersunk:

Minimum part size of 1” x 4”

  • Minimum length of the shortest side is 1”
  • Minimum length of the longest side is 4”

Maximum part size of 14” x 46”

  • Maximum length of the shortest side is 14”
  • Maximum length of the longest side is 46”

Be sure to check our Processing Min/Max chart for more information on minimum and maximum geometry for your specific material, thickness, and part size.

Materials Available for Countersinking

At this time, we offer 7 materials for countersinking:

File Setup and Design Considerations

Confirming countersink placement in our app

When you upload your file to our app, you’ll be able to view your part in a 3D model to check that the final product will function the way you intended. Use this model to make sure your countersinks are placed in the correct orientation on your part. Countersinks can be placed on the top or bottom face of a part, so it’s important to check carefully that they are indicated on the correct face.

Indicating countersunk holes

When setting up your file for countersinking, keep in mind that you only need to include the inner circumference of the hole (called the Minor) that is to be countersunk. Do not include the outer circumference (the size of the countersink, called the Major) in your file as that is what will be cut during the machining process, causing your hole to be too large to countersink. Your file should look like the one indicated here:

Hole size

The Major hole size should be the same size or slightly larger than the diameter of the hardware head you’re using. It’s best to use the exact diameter of the hardware head as your reference, but a good rule of thumb is to make the countersink 50% larger than the internal hole (Minor).

When selecting your hole operations for the desired hole in your design, we will automatically resize the hole to the required size as long as the starting hole is less than .500” in diameter. Please keep in mind that because they will resize, you will need to verify you have adequate clearance to other features and edges of the material.

You can see examples of countersinking sizing in the chart below. It’s important to note that these examples are based on sample hardware (linked in the chart) and hardware specifications and styles will vary based on the manufacturer.

Imperial/SAE Examples:

Hardware Size Hardware Head Diameter Countersink Minor Diameter Countersink Major Diameter Countersink Depth
10-32, ⅜” Hex Drive Flat Head Screws 0.411” 0.194” 0.411” 0.127”
¼-20, ⅜” Hex Drive Flat Head Screws 0.531” 0.250” 0.531” 0.161”

Metric Examples:

Hardware Size Hardware Head Diameter Countersink Minor Diameter Countersink Major Diameter Countersink Depth
M5 x .8mm, 14mm Hex Drive Flat Head Screw 10mm 5mm 10mm 2.8mm
M8 x 1.25mm, 12mm Hex Drive Flat Head Screw 16mm 8mm 16mm 4.4mm

Depth and angle

The depth of the countersink should be no more than 60% of the material thickness. Any deeper and you are risking the structural integrity of the material and part. If your countersink needs to exceed that depth, make sure the holes are spaced out far enough away from each other to prevent undue stress. Here, depth is defined as the distance from the surface of the material or top of the cone to the bottom of the cone. This is typically considered the head height for flat head bolt hardware specifications.

The angle of the countersink is dependent upon the hardware being used. Ideally, the hardware has at least 50% contact with the countersunk hole, but it doesn’t have to match exactly. The standard countersink angle for metric hardware is 90°, and the standard countersink angle for imperial hardware is 82°. We offer sizes in both angles.

Sizes available

The “Major” measurement shown here is the larger diameter at the top of the countersink, and the “Minor” measurement is the smaller diameter at the bottom of the countersink where the hole is at its smallest

When selecting your hole operations for the desired hole in your design, we will automatically resize the hole to the required size as long as the starting hole is less than .500” in diameter. 

Please keep in mind that because they will resize, you will need to verify you have adequate clearance to other features and edges of the material.

90° (Common for Metric bolts)

Metric Flat Head BoltMajorMinorDepth
M2 x 0.4mm4mm (0.157”)2.39mm (0.099”).074mm (.029″)
M2.5 x 0.45mm5mm (0.197”)2.49mm (0.103”)1.19mm (.047″)
M3 x 0.5mm6mm (0.236”)3.18mm (0.130”)1.35mm (.053″)
M4 x 0.7mm8mm (0.315”)4.04mm (0.164”)1.93mm (.076″)
M5 x 0.8mm10mm (0.394”)5.00mm (0.202”)2.44mm (.096″)
M6 x 1mm12mm (0.472”)6.35mm (0.255”)2.77mm (.109″)
M8 x 1.25mm16mm (0.630”)8.00mm (0.320”)3.94mm (.155″)

82° (Common for Imperial/SAE bolts)

Standard Flat Head BoltMajorMinorDepth
4-400.255” (6.48mm)0.130” (3.18mm).072″ (1.83mm)
6-320.307” (7.80mm)0.164” (4.04mm).082″ (2.08mm)
8-320.359” (9.12mm)0.193” (4.78mm).095″ (2.41mm)
10-240.411” (10.44mm)0.199” (4.93mm).122″ (3.10mm)
10-320.411” (10.44mm)0.199” (4.93mm).122″ (3.10mm)
1/4-200.531” (13.49mm)0.255” (6.35mm).159″ (4.04mm)
1/4-280.531” (13.49mm)0.255” (6.35mm).159″ (4.04mm)
5/16-180.656” (16.66mm)0.318” (8.08mm).194″ (4.93mm)
5/16-240.656” (16.66mm)0.318” (8.08mm).194″ (4.93mm)

More details are available from our preferred vendor, McMaster

What to Expect From Finished Parts

  • Parts may have oil/lubricant residue on the surface
  • Some light deburring may be required by the customer to remove sharp edges left by the countersinking process
  • Parts will not have a perfectly machined finish. Some scoring is expected. 
  • Powder coating will add .002”-.005” (.051mm-0.13mm) per side. We’ll adjust the hole size to account for this, but keep in mind that the fit may be tight on countersinks with powder coating

Pre-flight Checklist

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We proudly use hardware by PEM

Flush stud, M8 x 1.25, .472" Zinc plus Clear Chromate

Aluminum: 5052, 6061, 7075 Steel: Mild

SKUFH-M8-12
Thread SizeM8 x 1.25
Hole size in sheet (+0.003/-.0.000).315″
Minimum sheet thickness0.94″
Maximum sheet thickness.347″
Fastener materialSteel
Minimum distance hole C/L to edge0.378″
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..567″
Recommended panel materialSteel/Aluminum
Coating typeZinc
Length.472″
Aluminum material ranges (5052, 6061, 7075)0.100″-0.250″
Steel material ranges (CRS, HRPO, HR)0.104″-0.250″

Get an Instant Quote for Waterjet Cutting

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″