ISO 11363-1:2018

Overview

ISO 11363-1:2018 - "Gas cylinders - 17E and 25E taper threads for connection of valves to gas cylinders - Part 1: Specifications" defines the geometric specifications for two taper screw threads used to connect valves to gas cylinders. It covers the dimensions and tolerances for nominal diameters 17.4 mm (17E) and 25.8 mm (25E). The standard establishes thread form, pitch, taper and end‑finish so manufacturers and designers can produce compatible valve stems and cylinder necks.

Important exclusions: ISO 11363-1:2018 does not address mechanical strength, gas tightness or the capability for repeated assembly/disassembly. Gauge inspection procedures are covered separately in ISO 11363-2.

Key topics and technical requirements

• Thread diameters and reference planes: Nominal valve stem and cylinder neck dimensions are defined (e.g., major, pitch and minor diameters and reference lengths for 17E and 25E).
• Thread rotation: Right‑hand thread (tightens clockwise away from observer).
• Taper: Nominal taper ratio 3/25, taper angle 6° 52′, taper slope 12%.
• Thread profile: British Standard Whitworth (BSW) form with 55° thread angle; profile and thread‑height measurements are made perpendicular to the cone surface.
• Pitch: Nominal pitch 1.814 mm.
• Thread end finish: Valve stem requires a 45° chamfer 1–2 mm from the reference plane and a groove at the top; cylinder neck chamfer 1–2 mm from entry. The first (small end) thread must be fully formed with maximum clearance.
• Marking: Components threaded per this standard shall be marked “17E” or “25E” as applicable.
• Dimensional tables and figures: Detailed values and tolerances for both sizes are provided in tables and figures inside the document.

Practical applications

• Ensuring interchangeability of cylinder valves and necks across manufacturers.
• Guiding CNC and manual machining of valve stems and cylinder necks.
• Serving as a reference for design engineers, OEMs, cylinder manufacturers, valve producers and thread tool makers.
• Supporting conformity assessment, incoming inspection and quality control (with gauge inspection per ISO 11363-2).
• Useful for safety engineers and maintenance organizations verifying correct fittings for compressed gas systems.

Who uses this standard

• Gas cylinder manufacturers and repair shops
• Valve manufacturers and component suppliers
• Mechanical designers and product engineers
• Inspection laboratories and certification bodies
• Procurement and quality assurance teams in industries using compressed gases (industrial gases, welding, medical, specialty gases)

Related standards

• ISO 11363-2 (Gauge inspection)
• ISO 11116-1 / ISO 10920 (related taper thread specifications)
• ISO 68-1 (basic screw thread profiles)

Keywords: ISO 11363-1:2018, 17E, 25E, taper threads, gas cylinders, valve connection, thread profile, Whitworth, thread pitch, taper ratio.