How to choose between 9.53, 12.7 and 15.24 mm strand
Diameter selection is a system decision, not a preference for a larger strand. This guide sets out the five inputs that decide it and the mistakes that appear when strand is chosen before the anchorage is fixed.
Diameter follows the required force and the approved system — not the other way round.
Strand diameter is selected to deliver the prestressing force the designer needs, within the anchorage, duct and jack that the project has approved. A larger strand carries more force per tendon, which reduces tendon count and anchorage congestion, but it also requires a larger anchorage, a larger duct and a higher-capacity jack. Global Overseas lists 9.53 mm, 12.7 mm and 15.24 mm low-relaxation strand so that buyers can match common project schedules and regional specifications, but the correct diameter for a given structure is the one in the approved drawings.
The five inputs that decide diameter
Diameter is not chosen from a catalogue; it falls out of five project inputs. Work through them in order and the answer is usually unambiguous.
What the three standard diameters are for
The three diameters Global Overseas manufactures to ASTM A416 Grade 270 cover most of the market, and their minimum breaking loads differ substantially: 9.53 mm is 102.3 kN, 12.7 mm is 184 kN, and 15.24 mm is 260 kN.
The mistakes that cost money
Most diameter problems are created before the RFQ is sent, and they surface as change orders after the order is placed.
What to put in the RFQ
State the nominal diameter, the standard and grade, the relaxation class, the quantity, the coil weight or cut length, the packing method and the destination port. For post-tensioning orders, add the anchor type, the wedge or jack interface and the duct type. With those fields complete, the supplier can confirm compatibility rather than guess.
Common questions on diameter
Which diameter is most common?
For large-scale bridge and building projects, 15.24 mm (0.6 inch) low-relaxation strand is the most commonly specified diameter. It carries the highest force per tendon of the three standard sizes, which reduces tendon count and anchorage congestion. 12.7 mm is widely used where a balance between force per tendon and anchorage size is needed, and 9.53 mm suits precast elements, sleepers and smaller tendons.
Can I switch diameter without changing the anchorage?
No. The anchorage and wedge are sized for the strand, so a diameter change is an anchorage change. Substituting a different diameter against an approved anchorage is a specification deviation, and it must be confirmed with the engineer and the anchorage supplier before the order is placed.
What are the minimum breaking loads?
For ASTM A416 Grade 270 low-relaxation strand, Global Overseas supplies 9.53 mm at a minimum breaking load of 102.3 kN, 12.7 mm at 184 kN, and 15.24 mm at 260 kN, each with minimum elongation of 3.5 percent.
Need this confirmed for your order?
Send the standard, diameter and quantity with your inquiry and the relevant document set will be confirmed before shipment.
Contact our engineersNot sure which diameter your drawing calls for?
Send the drawing and the standard — our engineers will confirm the diameter, anchorage compatibility and lead time.