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How to call out a countersink on a drawing

Updated July 20, 2017

A countersunk hole is a cone-shaped recess in an object, designed to accommodate a flathead screw such that the head of the screw is flush with the surface of the part. Countersunk holes are represented in engineering drawings in a standard way to make the production and manufacturing process easier and more efficient.

Inches or standard measurement

Draw the leader, or dimension line, with the arrow just touching the edge of the outer circle of the countersunk hole. Draw the line radially, so that it points toward the centre of the hole, and if extended it would pass through the centre point.

Write the dimensions of the countersink, giving first the diameter of the drill hole, then the angle of the countersink, followed by the diameter symbol and the diameter of the larger hole. This dimension can be given either with a diameter symbol first, or with the word DRILL after the first diameter.

Add the number of holes, if there are more than one. It is only necessary to dimension one of the holes. Use the format 3 HOLES, where 3 is the number of holes.

Metric

Draw the leader, or dimension line, with the arrow just touching the edge of the outer circle of the countersunk hole. Draw the line radially, so that it points toward the centre of the hole, and if extended it would pass through the centre point.

Write the number of holes. Use the format 3X, where 3 is the number of holes. Follow with the diameter symbol and the diameter of the hole. It is only necessary to dimension one hole.

Draw the ASME countersink symbol. Follow with the diameter symbol and diameter of the larger countersink hole. Add the angle of the countersink.

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About the Author

Mina Law is a freelance writer working in Pittsburgh, Pennsylvania since 2010. Her stories and articles have appeared at Cafe Irreal and Archeojobs. She holds a Bachelor of Arts in classics, and Medieval and Renaissance studies from the University of Pittsburgh, as well as a Nonfiction Writing Certificate. Law is pursuing a Master of Arts degree in journalism and communications from Point Park University.