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How to countersink a screw

November 15, 2018

Screws have heads, which in some cases have to stick out. In most cases, however, the aim is to countersink the head flush with the surface of the material. How to countersink a screw is explained in this article.

Countersunk screws have different heads. Screws that can be countersunk have the following screw heads:

  • countersunk head
  • lens countersunk head
  • cylinder-head
  • round head
  • hexagonal

Nuts can also be countersunk.

If you need to cut an internal thread in the drill hole for the screw, countersinking is the second step in the work process after you have drilled (and deburred) the drill hole. Once you have made the countersink, all you have to do is cut the internal thread. How to do these other steps is explained in our article "How to cut an internal thread in three steps".

The right countersink

You need a suitable countersink to countersink screws. Countersinks have a countersink angle of 90° (and for US standard 82°) for countersinking screws, e.g. the countersink angle for rivets is 120°. For the flat countersink, the countersink angle is 180°.

Screw Countersink
Countersunk head screws Countersink
Lens countersunk head screws Countersink
Cylinder-head screws Flat countersink
Round-head screws Flat countersink
Hexagon screws Flat countersink
Nuts Flat countersink
Countersunk screw in through hole

Countersunk screw in through hole

Cylinder-head screw in through hole

Cylinder-head screw in through hole

In our last blog post "The structure and application of countersinks" we described the structure and the different fields of application of countersinks in detail.

Countersinks and flat countersinks from RUKO

Countersinks and flat countersinks from RUKO

Flat countersinks have a fixed guide at the tip, which is inserted into the pre-drilled hole. This ensures stable guidance and precise working.

Countersinking with the countersink

You only need the diameter of the screw head. The best way to measure is to use a calliper.

When you have measured the diameter of the head, use the corresponding countersink with a lager diameter. Use the tool to make your countersink.

Countersinking depth

When countersinking a screw you cut with the countersink the depth by feel.

Lowering with the flat countersink

With the flat countersink, in addition to the head diameter, you also need the height of the hexagon socket screw to determine the countersink depth.

With a hexagon head screw (also called a wrench screw), which you can only tighten with a socket wrench or pipe wrench, you need a larger diameter for the countersink. For this you need to measure the diameter of your wrench.

When selecting the correct flat countersink, note that it is available in two versions: for through hole and thread core hole. With the through-hole there is a thread only in the second material. With the threaded core hole, both materials have a thread.

The diameter of the fixed guide for the through hole is larger than for the thread core hole. For a through hole for thread M12 (grade fine) the pin diameter is 13.0 mm. For the thread core hole, the pin diameter for the M12 thread is 10.2 mm.

The diameter of the fixed guide for the through hole is larger than for the thread core hole

The diameter of the fixed guide for the through hole is larger than for the thread core hole


There are countersinks made of HSS, HSSE-Co 5 and hard metal, which are finished with a TiN, TiAlN or RUnaTEC coating, for different fields of application. The following overview will help you to find the right countersink.

Make sure that the cutting speed is very low when lowering, especially when using hard materials such as hardwood or metal. Apply less force when processing, because countersinking only requires light pressure.

Conclusion and summary

Sinking a screw is basically very simple.

You need the diameter of the head of your screw and off you go. With the head's diameter, whether for countersinks or flat countersinks, you have the measurement for the selection of the right countersink.

In the application, you drill with the countersink up to the maximum diameter. For the flat countersink, you will also need to measure the height of the screw head to know how far into the workpiece you need to drill and what type of hole (through hole or thread core hole) you need to drill. Then, you can countersink your screw in the material flush with the surface.

You can find our countersink 90° and 82°, and flat countersink at Products > Countersink.

If you have trouble finding the right sheet drill, please do not hesitate to contact us.

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