We are independent & ad-supported. We may earn a commission for purchases made through our links.

Advertiser Disclosure

Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.

How We Make Money

We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently from our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is a Drill Collar?

By David Larson
Updated May 17, 2024
Our promise to you
About Mechanics is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At About Mechanics, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

A drill collar is a device used in the drilling of oil wells for weighting the drill bit, enabling it to drill through rock. It is a bar made of solid steel, either plain carbon steel or a non-magnetic steel alloy, drilled lengthwise to permit the passage of drilling fluids. A drill collar forms the lowest element of a drill string, which encompasses all the elements of a down-hole process from the surface to the rock bit.

These devices are typically 31 feet (about 9.45 m) long and threaded at both ends, male at one end and female at the other, to allow multiple drill collars to be joined above the bit assembly. The number of drill collars attached to a drill string will depend upon the material composition of the strata at the drill site and the likely depth of the well. A relatively shallow well with less dense geologic structure through which the bit must pass will require fewer drill collars than a deep shaft through dense material.

Typically, drill collars will be consistent in length but may vary in diameter, and their outside configuration may be slick or spiral. The outside diameter may vary from about 3 inches (7.62 cm) to 11 inches (27.9 cm) and greater. The reference to slick or spiral outer configuration refers to the machining of the outside surface of the collar.

A slick surface simply refers to a collar machined to a uniform cylindrical shape. A spiral collar is machined to have a helical pattern incised into its outer surface. The purpose of the helical grooves is to permit the passage of debris up the drill string and prevent its becoming stuck in the well hole.

The pressure applied to the drill bit assembly by the collar and other elements of the drill string must be carefully regulated for effective drilling. The weight of the drill string is monitored at the surface, and the operator slowly lowers the drill string into the hole until the registered weight changes. If the bit is resting on the bottom of the hole and the monitor shows a reduction of 10,000 pounds (4,540 kg), there should be a corresponding increase in pressure on the drill bit assembly.

Equipment used in conjunction with drill collars in oil well drilling includes drill collar slips, drill collar clamps, and die collars. The drill collar slip is a device used to handle drill collars while attaching new sections, and is adjustable to a variety of diameters. Drill collar clamps are also used while handling drill collars to prevent their being dropped into a well shaft. In the event a drill string is broken and a drill collar and bit are at the bottom of the shaft, the die collar is lowered and with a self-tapping bit, threads an attaching connection into the drill collar, allowing its retrieval.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Discussion Comments

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.