Standards reference
ISO 273 — Clearance Holes for Bolts and Screws
Reference overview of ISO 273 clearance-hole series and how DraftFit uses them in the metric thread and bolt tool.
Reference
ISO 273:1979
ISO 273:1979 was reviewed and confirmed in 2024 and remains current.
What it specifies
ISO 273 specifies general-purpose clearance-hole diameters for bolts and screws using fine, medium and coarse series across a broad range of metric thread sizes.
DraftFit behavior
DraftFit treats fine, medium and coarse clearance-hole series as explicit selections rather than inventing unrelated tolerance grades for the hole diameter.
Calculator
Metric Thread & Bolt Calculator →This page is an orientation aid, not a reproduction of the standard. Obtain and use the controlled standard required by your project.