Clearance hole sizes for inch and metric bolts and screws in all three fit classes, plus a calculator that turns a clearance hole into the positional tolerance it can carry (and back).

Clearance Holes

Positional Tolerance Calculator

Pick a screw and a fit to fill in F and H, or type your own values. Results use the formulas in ASME Y14.5 Appendix B and assume both the hole and the fastener are at MMC.

in in in

Position tolerance this hole allows

Hole needed for a position tolerance

in

How to read it: the drill is the nominal hole size, and the min–max range is the hole tolerance that the standard applies: ISO 286 H12 for close, H13 for normal and H14 for loose. Normal is the usual default. Use close where parts locate off the screws or the pattern is tight, and loose for weldments and stacked tolerances.

Floating vs. fixed fasteners: a floating fastener passes through clearance holes in every part (bolt and nut), so each part can use the full T = H − F. A fixed fastener is held in one part (screw in a tapped hole, or a stud), so the same clearance is shared between both parts and each gets T = (H − F) / 2. You can also split it unequally, H = F + T₁ + T₂. These formulas assume a projected tolerance zone on the tapped hole. Without one, the tapped hole’s axis can tilt, and Y14.5 uses H = F + T₁ + T₂(1 + 2P/D) instead, where P is the maximum thickness of the part with the clearance hole and D is the minimum thread engagement.

About F: the calculator and the chart’s position tolerance line default F to the screw’s nominal diameter. A real screw’s maximum major diameter is a little smaller (1/4-20 UNC-2A is 0.2489 in, M6×1 6g is 5.974 mm), so nominal is slightly conservative. Enter the actual maximum major diameter for exact figures.

Data Sources: Hole sizes are transcribed directly from ASME B18.2.8-1999, Clearance Holes for Bolts, Screws, and Studs: Table 2 for inch fasteners (#0 through 1-1/2 in, the standard's full stated scope) and Table 3 for metric fasteners (M1.6 through M100). The standard states that its metric holes agree with ISO 273, whose fine, medium and coarse series match the close, normal and loose fits here; ISO 273 also lists intermediate sizes (such as M3.5, M18 and M22) and sizes up to M150, which this chart leaves out rather than estimating them. Hole tolerances are per ISO 286 (H12/H13/H14), as B18.2.8 Sec. 3.3 specifies.

Positional tolerance formulas are from ASME Y14.5-2009, Nonmandatory Appendix B: floating fastener (B.3), fixed fastener with a projected tolerance zone (B.4), and the tilt allowance when no projected tolerance zone is used (B.5).