Bits ‘n Pieces – The Driller’s Blog

When is a 6 inch Reaming Shell Not a 6 inch Reaming Shell?

Posted by Rod McCoremick on Jul 24, 2019 11:00:00 AM
Rod McCoremick

Many of our blog topics come from real-life situations, either from reports on onsite visits or directly from our customers. They represent the types of issues that many of our customers are facing so we use these opportunities to explore possible solutions or explanations. This blog is about industry standards within the diamond drilling world.

A customer recently contacted our sales department asking about our 6 inch reaming shells. The sales representative provided him with technical information, including a technical sheet, catalog, etc. The customer received the reaming shell and sent us a photo he took of the product next to a measuring tape. He pointed out that the actual reaming shell was only 5 inches in height and wondered if we had sent him the wrong size of reaming shell.


The answer is no. He did get the correct part, however, there is no easy explanation as to why a 6 inch reaming shell is not quite 6 inches in length. It is simply an industry standard. For reasons that are not clear to anyone, much of the equipment used in diamond drilling is not the size it is described as being.

In the example of reaming shells, there are 3 common or “standard” lengths in diamond drilling: 6 inches, 10 inches, and 18 inches. None of these actually measure 6 inches, 10 inches or 18 inches. To complicate things further, the lengths vary according to the diameter. In the case of a 6 inch White Rhino reaming shell, when you measure it shoulder to shoulder a:

  • BWL 6 inch White Rhino actually measures 4 ½ inches
  • NWL 6 inch White Rhino actually measures 5 ¼ inches
  • HWL 6 inch White Rhino actually measures 5 9/16 inches
  • PWL 6 inch White Rhino actually measures 6 ½ inches

None of the above is 6 inches in length because they are made to accommodate the standard industry size for each coring system.

A 10 inch White Rhino in BWL   measures 8-3/8 inches, while an 18 inch White Rhino in BWL and NWL measures 16 ¾ inches. You will also find some variation between suppliers. An 18 inch reaming shell from another supplier, in BO size, measures closer to 17 inches.

Reaming shells are not the only piece of equipment affected. A 5 foot core barrel is not actually 5 feet in length. It is however, it is made to accommodate a core sample that is 5 feet long or 1.5 meters in length. The most important thing to remember is that the difference is minor and the number used is simply a label that differentiates between the shortest ( 6 inch) the medium length (10 inches) and the longest (18 inches). Most drillers are aware or perhaps have never actually measured their equipment precisely.

You can visually distinguish from a 6 inch shell and a 10 inch shell. A 6 inch reaming shell has 1 ring, a 10 inch shell has 2 rings and an 18 inch reaming shell has 3-4 rings.

If you were to take out your measuring tape and measure a lot of drilling equipment, you would find that most equipment varies in a similar way. Sometimes people new to diamond drilling are not aware and wonder if they ordered the right size once they measure it. For simple questions like these, or for more difficult ones, you can always contact our technical support team. They have a wealth of onsite experience and information in their pockets ready to share.

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Topics: Basic drilling information, How to choose equipment

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