Hexagonal Kelly: Specifications and Selection Guide

A hexagonal Kelly is a hollow, externally hexagonal drill-string component that transfers rotary-table torque to the drill string while allowing the string to move vertically during drilling. To select one, match its across-flats dimension, overall length, bore and wall requirements, connection interfaces, and material requirements to the rig and drilling program. These details are project-specific: a dimension that suits one rotary table or connection does not automatically suit another.

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This guide explains the specifications buyers should confirm, how to compare options, and what information to include in a supplier inquiry. Any dimensions used below as examples are illustrative only, not standard sizes or recommendations.

Who This Guide Is For

This guide is intended for drilling contractors, oilfield equipment distributors, procurement teams, and engineering personnel sourcing a hexagonal Kelly for a particular rig or drilling application. It is also useful when replacing an existing component, assessing a drawing, or comparing quotations from steel pipe manufacturers and suppliers. The best starting point is the equipment interface and the approved drilling specification, rather than a general product description.

How a Hexagonal Kelly Works

Shape and core function

The Kelly sits in the rotary drive arrangement and connects the surface drive to the drill string. Its hexagonal outside profile engages with a matching drive element, allowing torque to be transmitted as the rotary system turns. The hollow body provides a passage for drilling fluid when the configuration and connections are designed for that purpose.

During drilling, the Kelly also moves through the rotary drive as the drill string advances. The component therefore needs to suit both the rig’s drive arrangement and the intended drilling operation. Exact compatibility depends on the equipment design, connection details, and operating requirements.

Specifications to Confirm Before Ordering

Across-flats dimension and profile

Across-flats, often abbreviated as AF, is the distance between two opposite flat faces of the hexagonal section. Confirm the required AF dimension from the rig documentation, an approved drawing, or a verified measurement of the existing component. Also establish the profile and dimensional tolerances required by the mating drive equipment; a nominally similar hexagonal shape is not enough to establish fit.

Overall length, bore, and wall requirements

Specify the required overall length and any relevant working-length or end-to-end measurement conventions. Confirm the bore requirements, including whether the internal passage must meet a particular drawing or drilling-fluid arrangement. Wall thickness and section details should be reviewed against the design and service requirements by qualified engineering personnel, not selected from a generic online example.

For clarity, a hypothetical inquiry could identify an overall length of 11 m, an AF dimension of 100 mm, and a wall thickness of 25 mm. These three figures are examples for illustrating how units can be stated; they are not universal Kelly specifications or a recommendation for any rig. Buyers should use approved project values and agree on measurement points and tolerances with the supplier.

Connections, material, and documentation

List the connection type, size, and relevant interface details at each end, using the equipment drawing or existing component as the reference. State the required material grade or governing project specification where applicable, and confirm what material documentation the purchase requires. Do not assume a grade, connection, or inspection requirement from the term “hexagonal Kelly” alone.

Depending on the application and purchase specification, buyers may also request dimensional inspection records, material traceability documents, or other agreed quality records. Define these requirements before placing an order so that the supplier can confirm feasibility and include them in the quotation. Any inspection or test should be described by its applicable standard, scope, and acceptance criteria.

Match the Kelly to the Application

Start by identifying the rig and rotary drive arrangement where the Kelly will operate. Verify that the external hex profile and AF dimension match the drive interface, then confirm that the length and connections suit the planned drill-string configuration. If replacing a worn component, use the equipment drawing or a reliable dimensional inspection rather than relying only on visual comparison.

Consider operating conditions as well as physical fit. The drilling program, expected service environment, fluid requirements, and maintenance plan can affect the material and documentation requirements specified for the purchase. When these factors are not clear, involve the responsible drilling or engineering team before approving a final configuration.

A Practical Selection Framework

Collect the reference information. Obtain the rig or drive-system details, approved drawings, existing part information, and applicable project specifications. Record the source and revision of each document so the buyer and supplier are working from the same requirements.
Define the key dimensions. Confirm AF, overall length, bore, wall or section requirements, and the measurement points and tolerances that apply. Separate confirmed values from values that still need engineering review.
Specify interfaces and materials. Document both end connections, the required material grade or specification, and any application-specific requirements. If a specification is not yet established, ask the responsible engineer to define it rather than substituting a supplier’s assumption.
Agree on inspection and records. List required inspections, documentation, acceptance criteria, and any hold or witness points before production or order confirmation. Ask the supplier to state clearly which items are included in the offer.
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Review the quotation against the request. Check that the offer addresses every dimension, interface, material requirement, document, quantity, and delivery point. Resolve deviations in writing before issuing a purchase order.

Price, MOQ, and Lead Time Considerations

Hexagonal Kelly pricing depends on the specified dimensions, material, connection work, inspection and documentation scope, order quantity, and delivery requirements. There is no reliable price or minimum order quantity to apply to every configuration without reviewing the requested specification. For a useful comparison, ask suppliers to quote the same technical scope and identify any exclusions or optional charges.

Lead time is likewise dependent on the configuration, production schedule, material availability, and agreed inspection or documentation requirements. Ask for a stated lead-time basis, such as the point at which the schedule begins, and confirm how drawing approval or changes affect it. For time-sensitive projects, request a written delivery plan rather than relying on an informal estimate.

Supplier Evaluation Checklist

Can the supplier review the drawing and confirm the requested dimensions and interfaces before quoting?
Does the quotation identify material requirements, inspection scope, documentation, and any deviations?
Can the supplier explain how dimensional requirements will be verified and reported?
Are quantity, packaging, delivery destination, lead-time assumptions, and quotation validity stated clearly?
Is there a clear process for resolving drawing questions or specification changes before manufacture?

When comparing manufacturers, evaluate the completeness and clarity of their technical response as well as the commercial offer. A low quotation may not be comparable if it excludes required inspection records, uses a different material basis, or assumes unconfirmed interfaces. Ask for discrepancies to be identified rather than silently accepted.

Common Selection Mistakes to Avoid

A frequent mistake is ordering by product name alone without confirming the AF dimension, length, or end connections. Another is treating an illustrative dimension or an old drawing as current without checking its revision and suitability for the rig. Buyers can reduce these risks by using a controlled specification and getting written confirmation of unresolved details.

It is also risky to leave inspection, traceability, or delivery expectations until after the quotation is approved. Requirements added late may affect cost, schedule, or what the supplier can provide. Put all mandatory technical and commercial conditions into the inquiry and review any exceptions before purchase.

Working with Longway

Longway supplies steel pipe products and can discuss hexagonal Kelly requirements with B2B buyers using their drawings, project specifications, and operating context. To support a focused review, share the required AF dimension, overall length, bore and section details, connection information, material specification, quantity, destination, and requested documentation. If any value is uncertain, identify it as pending confirmation rather than presenting it as final.

We can then review the requested scope and clarify which details need confirmation before a quotation is prepared. Buyers should evaluate the final offer against their approved equipment requirements and project acceptance criteria. This approach helps keep technical assumptions visible during sourcing.

Key Takeaways and Next Steps

A hexagonal Kelly transmits rotary torque through its external hex profile, but successful selection depends on much more than its shape. Confirm the AF dimension, length, bore and section requirements, connections, material basis, inspection records, and delivery terms against the intended rig and project specification. No example dimension should be treated as a universal standard.

For your next step, assemble the current drawing and operating requirements, mark any values that need engineering confirmation, and send the complete inquiry to potential suppliers. Contact Longway with your specification, quantity, and delivery requirements to discuss the requested configuration and quotation scope.