ISO 3438:2013

Overview

ISO 3438:2013 - Subland twist drills for holes prior to tapping screw threads - specifies standardized dimensions and tolerances for subland (stepped) twist drills used to create pilot holes before tapping metric screw threads (coarse pitch series). The standard covers two shank types: Morse taper shanks for thread sizes M8 to M30, and cylindrical shanks for thread sizes M3 to M14. All dimensions are given in millimetres and unspecified tolerances follow ISO 2768‑1 class “c”. ISO 3438:2013 complements ISO 2306 and includes an informative annex relating its symbols to the ISO 13399 cutting‑tool data model.

Key Topics

• Dimensional specifications: standardized cutting diameters, step diameters, overall and step lengths (symbols d1, d2, l1, l2, l3, etc.) for each covered thread size. Tables and figures in the standard define the exact values for each drill size.
• Shank types:
  • Morse taper shanks - conforming to ISO 296 for taper form, with a cone tolerance as defined in ISO 10899:1996.
  • Cylindrical shanks - dimensions specified for smaller metric thread sizes.
• Tolerances and units: all dimensions in millimetres; general tolerances per ISO 2768‑1 (class c) unless otherwise specified; specific tolerance zones (for example h8) used where required.
• Optional features: allowance for optional recesses and step profiles as shown in the standard’s figures.
• Data mapping: Annex A maps ISO 3438 symbols to the ISO 13399 series (cutting tool data representation), aiding digital tool data exchange.

Applications

ISO 3438:2013 is essential for anyone who designs, manufactures, buys, inspects, or uses subland twist drills for pre‑tapping operations:

• Tool manufacturers and designers - ensure drill geometries meet international dimensions and are compatible with tap requirements.
• CNC and machining shops - select correct pilot drills to produce accurate pre‑tap holes and consistent thread quality.
• Quality and inspection teams - verify drill dimensions and tolerances against a recognized standard.
• Procurement and specification writers - reference ISO 3438:2013 in purchase orders and technical drawings to ensure interchangeability.
• CAM/CAD and tooling data systems - use the ISO 13399 mapping for standardized digital tool libraries.

Related Standards

• ISO 2306 - complements ISO 3438 for tapping drills and related tooling.
• ISO 296 - specifies Morse taper dimensions for tool shanks.
• ISO 10899:1996 - referenced for cone tolerance and high‑speed steel drill specifications.
• ISO 2768‑1 - general linear/angular tolerances applied where unspecified.
• ISO 13399 series - cutting‑tool data representation (Annex A mapping for digital integration).

Keywords: ISO 3438:2013, subland twist drills, tapping screw threads, Morse taper shank, cylindrical shank, drill dimensions, metric threads, ISO 2306, ISO 13399.