Countersinking Design Guidelines

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

Countersinking Setup and Cost

Countersinking adds a $9 minimum to your line item. The $9 minimum applies to cart totals. Pricing starts at $3 per countersunk hole, with quantity discounts starting when you order more than one of an identical part.

Identical Part Quantity Holes per Part Total Holes Total Cost Breakdown
1 4 holes 4 $12 $3 per hole x 4 holes = $12
2 4 holes 8 $19.20 $3 per hole x 8 holes = $24 
$24 x 20% qty discount = $19.20
10 4 holes 40 $85.20 $3 per hole x 40 holes = $120 
$120 x 29% qty discount = $85.20
40 4 holes 160 $288.00 $3 per hole x 160 holes = $480 
$480 x 40% qty discount = $288

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”x4”

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

Maximum part size of 14”x46”

  • 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:

  • Aluminum 5052: .125”-.500” (3.18mm-12.7mm)
  • Aluminum 6061: .125”-.500” (3.18mm-12.7mm)
  • Aluminum 7075: .125”-.500” (3.18mm-12.7mm)
  • HDPE: .125”-.500” (3.18mm-12.7mm)
  • UHMW: .125”-.500” (3.18mm-12.7mm)
  • Delrin: .125”-.500” (3.18mm-12.7mm)
  • ABS: .125”-.500” (3.18mm-12.7mm)

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).

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 SizeHardwear Head DiameterCountersink Minor DiameterCountersink Major DiameterCountersink Depth
10-32, ⅜” Hex Drive Flat Head Screws0.411”0.194”0.411”0.127”
¼-20, ⅜” Hex Drive Flat Head Screws0.531”0.250”0.531”0.161”

Metric Examples:

Hardware SizeHardwear Head DiameterCountersink Minor DiameterCountersink Major DiameterCountersink Depth
M5 x .8mm, 14mm Hex Drive Flat Head Screw10mm5mm10mm2.8mm
M8 x 1.25mm, 12mm Hex Drive Flat Head Screw16mm8mm16mm4.4mm

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.


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.

90° (Common for Metric bolts)

4mm (0.157”)2.39mm (0.099”)
5mm (0.197”)2.49mm (0.103”)
6mm (0.236”)3.18mm (0.130”)
8mm (0.315”)4.04mm (0.164”)
10mm (0.394”)5.00mm (0.202”)
12mm (0.472”)6.35mm (0.255”)
16mm (0.630”)8.00mm (0.320”)

82° (Common for Imperial/SAE bolts)

0.255” (6.48mm)0.130” (3.18mm)
0.307” (7.80mm)0.164” (4.04mm)
0.359” (9.12mm)0.193” (4.78mm)
0.411” (10.44mm)0.199” (4.93mm)
0.531” (13.49mm)0.255” (6.35mm)
0.656” (16.66mm)0.318” (7.95mm)

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 .003”-.005” (.076mm-0.13mm). 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
Deburred vs non-deburred

Pre-flight Checklist

Before you upload your design files, be sure to go through our pre-flight checklist:

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