ISO 721:1991

Overview

ISO 721:1991 - Rock drilling equipment - Integral stems is an international standard that specifies the dimensional requirements for hexagonal monobloc (integral) drill stems used in rock drilling. Published as the second edition in 1991 (technical revision of ISO 721:1974), the standard defines the form and dimensional compatibility for 19 mm, 22 mm and 25 mm hexagonal integral stems with a forged collared shank, referencing the drawings (figures 1–3) and corresponding tables (tables 1–3) for exact dimensions.

Key topics and requirements

• Scope: Dimensions for hexagonal monobloc (integral) stems used in rock drilling.
• Sizes covered: Integral stems of 19 mm, 22 mm, and 25 mm hexagonal cross‑section with forged collared shank.
• Dimensional conformity: Each nominal size must comply with the dimensions illustrated in the specified figure and listed in the associated table (figure 1/table 1 for 19 mm, figure 2/table 2 for 22 mm, figure 3/table 3 for 25 mm).
• Combination guidance: Where recommended series of diameters (D) and lengths (L) cannot be used, the standard permits alternative combinations by using table values in different pairings (as noted in the standard).
• Interoperability: The standard is intended to ensure interchangeability between stems, bars and tool holders when used alongside related ISO components.
• Normative references: Links with ISO 722 (hollow hexagonal and round bars for bits) and ISO 723 (forged collared shanks and adapter sleeves) are referenced for complementary dimensions and components.

Applications and users

ISO 721:1991 is practical for:

• Manufacturers of rock drill bits and integrally stemmed drilling tools - to design and produce stems that meet international dimensional standards.
• Mining and construction companies - to specify compatible drill tools and ensure equipment interchangeability across fleets.
• Drill rig OEMs and maintenance teams - for selecting compatible replacement parts and adapters.
• Procurement and quality assurance - to create purchase specifications and perform dimensional inspections.
• Standards compliance officers and test laboratories - to verify conformity and support certification or acceptance testing.

Practical benefits include improved interchangeability, safety, streamlined inventory management, and clearer procurement specifications for rock drilling equipment.

Related standards

• ISO 722:1990 - Bars (hollow, hexagonal and round) for drill bits
• ISO 723:1990 - Forged collared shanks and adapter sleeves for hexagonal bits

Keywords: ISO 721:1991, rock drilling equipment, integral stems, hexagonal stems, forged collared shank, drill stem dimensions, drilling tool standards, mining equipment standards.