1.1 This specification covers two types of stress-relieved round high-carbon steel wire commonly used in prestressed concrete construction, as follows:

1.2 A supplementary requirement (S1) is provided for use where low-relaxation wire and relaxation testing for that product is required by the purchaser. The supplementary requirement applies only when specified in the purchase order.

1.3 This specification is applicable for orders in either inch-pounds units (as Specification A421) or in SI units (as Specification A421M).

1.4 The values stated in either inch-pound or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the specification.