Clearance Hole Size Chart — Metric & Inch

Clearance hole chart

Search for a fastener such as M6, M12, 1/4, or 1/2. Filter by metric or inch, then select the class used by your governing standard.

The table reports the recommended hole diameter, not the bolt diameter. The dataset keeps the source unit and shows the other unit as a calculated conversion. A nearest drill designation is intentionally left out until it can be mapped to a verified drill series; a convenient drill size must not silently replace the specified hole diameter.

Fine, medium, and coarse compared with close, normal, and loose

ISO 273 uses fine, medium, and coarse series for metric clearance holes. ASME B18.2.8 uses close, normal, and loose classes. These labels belong to different standards. Do not treat “fine” as the ISO name for “close,” or “medium” as the ISO name for “normal.” Compare actual diameters only after you confirm the required standard and fit.

The H12, H13, and H14 references in this chart describe hole-size tolerance bands associated with the clearance series. They are size-tolerance references, not positional tolerances. A clearance class does not define true position, perpendicularity, concentricity, or alignment of two holes.

Clearance hole versus tap drill

A clearance hole lets the fastener pass through without engaging the threads. A tap drill is smaller because it prepares material for a tap to form or cut internal threads. An M6 clearance hole and an M6 tap drill answer different manufacturing questions. Use the tap drill size chart when you are making a threaded hole.

Clearance hole versus counterbore

The clearance diameter controls the passage around the fastener shank. A counterbore is a larger, usually flat-bottomed recess that hides a socket-head cap screw or creates tool clearance. Specify both dimensions when needed: the clearance-hole diameter and the counterbore diameter and depth. One does not determine the other.

When the standard hole is not enough

Use the chart as a starting point, then check the design conditions. A tighter class can reduce assembly freedom, while a looser class can increase movement before clamping. Coatings, burrs, fabrication tolerance, punched or laser-cut edges, washers, and stack-up alignment can change the practical hole size. If two parts must align, define hole location and positional tolerance separately from clearance diameter. If the hole is made by a process with a larger or directional tolerance, verify process capability before releasing the drawing.

Related charts and tools

• Tap drill size chart for threaded holes.
• Drill bit size chart for available tool sizes and conversions.
• How to use Hole Wizard in SOLIDWORKS for feature setup.
• Bolt, wrench, and socket size chart for related fastener dimensions.

Sources

Metric terminology and values follow ISO 273:1979, which ISO lists as confirmed current in 2024. Inch terminology and recommended values follow ASME B18.2.8-1999 (S2021). Public Tabelic clearance-hole tables were used as a secondary cross-check for the selected rows.

Frequently asked questions

Does a clearance-hole class define positional tolerance?

No. It defines a recommended hole-size class. Specify hole location and positional tolerance separately when alignment matters.

Can I use an ISO medium hole as an ASME normal hole?

Do not assume that. The labels come from different standards. Compare the actual hole diameters and confirm the drawing, customer, or manufacturing requirement before selecting a class.

Should I select the nearest drill size?

Only after you confirm the required hole diameter, drill series, process tolerance, and material. The named standard value remains the design reference.