ASME B18.29.1 Helicoil (STI) Tapped Hole Chart (Inch Series)

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 (ASME B18.29.1 Helicoil (STI) Tapped Hole Chart (Inch Series)) 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 quantities and lead times for this family are confirmed at quotation — send your sizes, grades and quantities on the RFQ and the quote will carry a firm schedule. Sample availability is confirmed with the 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 is the STI tapped hole bigger than a normal 1/4-20 hole, and how do I check it?

Because the insert is wire, and the wire has to live somewhere. A helical coil insert is a diamond-cross-section coil of standard internal thread profile; when installed, its outer coils must seat into material that a standard 1/4-20 tap would have cut away. The collected chart shows the offset directly: a standard 1/4-20 minor diameter runs around 0.207 in, while the STI hole for the same thread starts at Dmin 0.315 in major with minor limits 0.2608–0.2704 — the wire cross-section occupies the band between. After the insert is in, the assembly presents a true 1/4-20 internal thread, so a standard bolt fits and the thread callout of the host drawing still works. Verification follows the standard, not feel: the hole is gauged before insert installation with STI GO and NOT GO (HI) thread gages plus a plain cylindrical gage, per System 21 of ANSI/ASME B1.3M. Two checks people skip: a normal 1/4-20 GO plug should NOT pass an STI hole — if it does, the wrong tap went in; and the D2 column is class-specific (Class 2B in this chart), so a different fit class is an RFQ line, not a field adjustment. The suggested-drill column (17/64 for 1/4-20 STI) sizes the pre-tap hole for the STI tap, and the 120° ± 5° countersink with set-down depth from the source note is what keeps the first coil and the chamfer from fighting at install.

Do I need this chart if I am buying the inserts rather than machining the holes?

Yes, for one paragraph of your drawing package. The insert supplier sizes inserts off your thread callout; the machine shop sizes the hole off ASME B18.29.1 — and the two meet only if the drawing says both. State on the drawing: the nominal thread the assembled insert must present (e.g. 1/4-20 UNC-2B after insert installation), the governing standard for the STI hole (ASME B18.29.1), the parent material (which drives tap style — bottoming for blind holes — and drill depth), and the insert length in nominal diameters, which this chart does not carry and which sets drilled depth together with the set-down note. The collected chart then does the rest: the shop picks the STI tap and suggested drill (the D2min–D2max and D1min–D1max limits govern acceptance), the gage crib orders STI GO/NOT GO gages per System 21, and inspection has objective limits instead of a trial-and-error fit against a loose insert. Quote the insert side with its own RFQ lines — free-running or screw-locking wire series, material, length — and the hole side is fully specified by the numbers on this page.