Overview
ISO 5969:1979 specifies dimensional deviations and tolerances on the threaded portion of ground thread taps used to produce pipe threads of the G series (ISO 228‑1) and Rp series (ISO 7‑1). The standard defines how the major diameter and pitch diameter of ground taps must relate to the corresponding limits for internal threads (conventionally called “nuts”), and gives calculation examples and tabulated values for common sizes.
Key topics and technical requirements
- Scope: Tolerances apply to the threaded portion of ground taps intended for production of ISO 228‑1 (G - parallel pipe threads) and ISO 7‑1 (Rp - parallel pipe threads where pressure-tight joints are made on the threads).
- Tolerancing principle: Tap tolerances are expressed in terms of the nut pitch‑diameter tolerance unit t (equal to the nut pitch diameter tolerance TD2). Tap deviations are defined as fixed fractions of t.
- Specified deviations (summary):
- G series (ISO 228‑1): Js = +0.3 t, Em = +0.2 t, Es = +0.4 t (tap pitch‑diameter lower/upper deviations and major‑diameter lower deviation defined relative to nut limits).
- Rp series (ISO 7‑1): Js = −0.3 t, Em = −0.3 t, Es = −0.1 t.
- Angle tolerance: Thread flank angle tolerance is ±30′ (30 minutes).
- Minor diameter: Not specified by this standard for taps.
- Cumulative pitch error (TP): Assessed as per ISO 2857 (ground thread taps), referenced by the standard.
- Tables and examples: Numeric tables provide basic diameters and calculated min/max pitch and major diameters for a range of pipe thread sizes (including worked examples for G 1/2 and Rp 1/2).
Applications and who uses it
- Tap manufacturers use ISO 5969 to design and grind tap profiles and set allowable dimensional limits for production.
- Tooling and gauge designers rely on the tolerances to make acceptance gauges and quality-control fixtures for pipe-thread taps.
- Quality inspectors and production engineers use the standard to verify compliance and ensure interchangeability with nuts specified to ISO 228‑1 or ISO 7‑1.
- Plumbing, hydraulic and pipe-fitting industries benefit from consistent mating between male and female connections produced with standardized taps.
Related standards
- ISO 228‑1 - Pipe threads where pressure-tight joints are not made on the threads (designation, dimensions, tolerances).
- ISO 7‑1 - Pipe threads where pressure-tight joints are made on the threads.
- ISO 2857 - Ground thread taps for ISO metric threads (manufacturing tolerances and cumulative pitch error).
- ISO 2284 - Hand taps for pipe threads (general dimensions and marking).
Keywords: ISO 5969, ground thread taps, pipe threads, G series, Rp series, tolerances, major diameter, pitch diameter, ISO 228‑1, ISO 7‑1, tap manufacturing.
Open preview (PDF)Ground thread taps for pipe threads G series and Rp series — Tolerances on the threaded portion