ANSI, ISO Thread Designations and References

Documents

Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.

Quotation

• The fastener family (ANSI, ISO Thread Designations and References) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
• Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
• Quantity per size and your target delivery date.
• Destination country, and any required documents (for example a mill test certificate) so the quote includes them.

Sample & supply

Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.

Storage & shipping

Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.

Why do pipe thread designations like NPT, NPTF and NPS look so similar but behave so differently?

Because the letter after NP is the whole story. NPT — National Pipe Taper — is the taper thread that seals by wrench-tightening metal-to-metal on the flanks; NPTF is the dryseal variant with flattened crests and roots designed to seal without sealant; the NPS series (NPSM, NPSC, NPSF, NPSI) are straight threads that do not seal on the thread at all — they are for mechanical joints or, in the dryseal fuel/intermediate versions (NPSF/NPSI), for sealing with a gasket or O-ring at a shoulder. The chart's reference column shows they even come from different documents (B1.20.1 vs B1.20.3 family). Substituting a straight for a taper thread in a pressure joint leaks; substituting NPTF for NPT usually works mechanically but not always with used fittings. Read the full callout on the drawing, match it exactly, and quote per RFQ — thread-series substitution on pressure work is not ours to assume.

What is the difference between UNR, UNJ and the plain UN series in the chart?

All three are Unified inch threads with the same dimensions; the suffix changes the root contour. Plain UN has the standard sharp-ish root; UNR mandates a rolled (smooth, radius not less than 0.108P per the chart) root that improves fatigue life without changing mating dimensions; UNJ goes further with a larger controlled root radius (0.15011P to 0.18042P, as the chart's description spells out) — and because the bigger radius consumes space on the mating internal thread, UNJ bolts and nuts are a matched system, common in aerospace. So a callout of 1/4-20 UNJ vs plain UN affects which mating parts and which inspection apply, not the wrench size. When a drawing carries UNJ or UNR, quote it verbatim: substituting plain UN threads would silently delete the fatigue requirement the callout exists to enforce.