A 6 3/4 inch drill collar has a nominal outside diameter of 6.750 inches, but its actual dimensions and weight depend on the bore, connection design, overall length, machining allowances, and end configuration. In practical purchasing, I do not treat “6 3/4 inch” as a complete specification because two collars with the same outside diameter can have different internal diameters and weights. For a reliable quotation, I recommend confirming the required outside diameter, inside diameter, tool joint connection, length, steel grade, and whether the weight is required as theoretical body weight or finished shipping weight.
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As a reference, a plain steel body with a 6.750-inch outside diameter and a 3.000-inch inside diameter has an approximate theoretical steel weight of 97.6 lb/ft before accounting for connections, upsets, grooves, hardbanding, and other features. If the same outside diameter uses a smaller 2.875-inch bore, the theoretical body weight increases to approximately 103.6 lb/ft. These figures are engineering estimates rather than a substitute for the final manufacturing drawing or inspection record.
The primary dimension is the nominal outside diameter, commonly written as 6 3/4 inches or 6.750 inches. This dimension determines the approximate collar size used in the bottom-hole assembly and affects stiffness, available annular clearance, and the amount of weight that can be placed above the bit. The finished outside surface may also include spiral grooves, wear-reducing features, or hardbanding, so the purchasing specification should define whether the stated diameter refers to the base body or the finished outside profile.
The inside diameter is not automatically fixed by the outside diameter. Manufacturers may produce different bore sizes to accommodate the required hydraulic flow area, pressure-drop target, connection design, and mechanical requirements of the drilling assembly. A smaller bore generally leaves more steel in the collar wall and increases theoretical weight, while a larger bore can reduce weight and increase internal flow area, subject to the design limits of the collar.
For this reason, I ask buyers to provide the required inside diameter or the drilling system’s preferred bore before confirming a 6 3/4 inch drill collar. If the bore is not specified, a supplier may only be able to provide a budgetary estimate. The final selection should be checked against the BHA design, circulating system, connection requirements, and applicable purchasing standards.
Drill collars are commonly ordered in long individual sections, but the exact finished length is project-specific. A 30 ft collar is a useful example for estimating material quantity, but buyers should not assume that every 6 3/4 inch collar is supplied at exactly that length. Length can be affected by the requested connection, end facing, machining allowance, handling limitations, transport requirements, and the buyer’s BHA layout.
The two ends are machined with compatible rotary-shouldered connections. Connection type, pin and box dimensions, shoulder design, makeup requirements, and gauge protection can materially affect the final length and weight. I therefore recommend specifying the complete connection designation rather than requesting only a “6 3/4 inch drill collar.”
For an initial estimate, the theoretical steel body weight can be calculated from the outside and inside diameters. A commonly used approximation for steel is: weight per foot ≈ 2.67 × (OD² − ID²), where OD and ID are measured in inches and the result is expressed in pounds per foot. This formula estimates the cylindrical body only and does not include the additional or reduced material created by connections, chamfers, grooves, hardbanding, or other machining.
| Example configuration | Approximate theoretical body weight | Illustrative 30 ft body weight |
|---|---|---|
| 6.750 in OD × 3.000 in ID | 97.6 lb/ft | 2,928 lb |
| 6.750 in OD × 2.875 in ID | 103.6 lb/ft | 3,108 lb |
The table demonstrates why the bore must be confirmed before a buyer compares quotations. The 3.000-inch-bore example produces approximately 2,928 lb for a theoretical 30 ft body, while the 2.875-inch-bore example produces approximately 3,108 lb. The finished collar weight may differ because the connection ends and any additional surface treatment are not represented by the simple body calculation.
Wall thickness is calculated from the difference between the outside and inside diameters, so even a relatively small bore change can influence the amount of steel in the body. The calculation also assumes a typical steel density, while actual material density and manufacturing tolerances can create small variations. For production purchasing, I use the approved drawing and the supplier’s measured data rather than relying only on a nominal formula.
Connection areas are not simple uninterrupted cylinders. Pins, boxes, shoulders, reliefs, recesses, and end treatments change the local cross-section and may add or remove material compared with the plain-body estimate. Spiral grooves can reduce the external steel volume, while hardbanding or other applied materials may add weight and alter the finished outside profile.
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The weight per foot is useful for estimating, but the total shipping weight also depends on the actual finished length. A collar supplied at 31 ft will naturally weigh more than one supplied at 30 ft when the cross-section is otherwise equivalent. Packaging, protectors, skids, and bundled quantities can further affect the logistics weight even though they are not part of the drill collar itself.
A 6 3/4 inch drill collar is generally selected when the drilling assembly requires a substantial stiff tubular member and controlled weight transfer near the bit. Its suitability depends on the hole size, casing program, directional profile, drilling parameters, hydraulic design, and clearance requirements. I do not recommend choosing the collar by diameter alone because the correct BHA balance requires the collar to work with the drill pipe, stabilizers, jars, motor or rotary steerable equipment, and bit.
In directional or deviated drilling, buyers may evaluate spiral versus slick configurations according to their intended use and downhole conditions. Spiral designs can be considered when reducing contact area and differential-sticking risk is part of the BHA strategy, while slick designs may be preferred where a continuous cylindrical body is required. These are application decisions that should be reviewed with the drilling engineer rather than treated as universal advantages.
When I prepare or review a drill collar inquiry, I look for a complete technical request. The following information helps prevent an inaccurate quotation or a late design change:
I also recommend separating three weight descriptions in the purchase order: theoretical body weight, finished individual collar weight, and total packed shipping weight. This distinction is important for rig handling, transport planning, crane selection, and freight budgeting. If a quotation gives only one unexplained weight, the buyer should ask which basis was used.
At Longway, I approach a 6 3/4 inch drill collar inquiry by first matching the dimensional requirement with the intended BHA application. I can help organize the requested OD, ID, length, connection, material, surface treatment, inspection, and packing information into a clear manufacturing specification. Where the buyer has not finalized the bore or connection, I recommend confirming those engineering inputs before treating the price and weight as final.
For export and project purchasing, clear documentation is as important as the steel product itself. I can coordinate the information needed for dimensional confirmation, production communication, inspection planning, marking, thread protection, and shipment preparation, subject to the agreed scope of supply. The exact documents and inspection level should be defined in the purchase order so that both sides have the same acceptance criteria.
The dimensions and weight of a 6 3/4 inch drill collar cannot be identified accurately from the outside diameter alone. The nominal OD is 6.750 inches, but the final weight must be calculated or measured using the specified bore, length, connection design, and finished features. For a practical next step, I recommend sending Longway the required OD, ID, length, connection, material, application, quantity, and inspection expectations.
With those details, I can help establish whether the requested weight is theoretical, finished, or packed, and help reduce ambiguity before production begins. A complete specification gives the buyer a more reliable quotation, clearer logistics planning, and a better basis for comparing drill collar suppliers.
Contact Longway with your 6 3/4 inch drill collar requirements for a project-specific dimensional, weight, and supply review.
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