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Dust port and hose size standards explained
Dust extraction has grown up around a handful of recurring sizes rather than one clean standard, so matching a tool to a hose means knowing which family of sizes you are in.
Two worlds: high pressure and high volume
Shop vacuums move a small volume of air at high suction through a narrow hose, typically 1.25 inch, 1.5 inch or 2.5 inch. Dust collectors move a large volume of air at low suction through a wide duct, typically 4 inch, or in metric 100 millimetres. The two are designed for different jobs, so their fittings are different sizes.
A hand sander or router runs happily on a narrow vacuum hose. A table saw or planer that throws chips needs the volume of a 4 inch collector. Matching starts by deciding which of these two systems the tool belongs to.
Common shop-vac sizes
Shop-vac hoses cluster around 1.25 inch, 1.5 inch and 2.5 inch outer working diameters, though the exact figure varies by brand because these are nominal rather than tightly standardised. In metric power tools the tool port is often 27, 35 or 36 millimetres, sizes used across DeWalt, Bosch, Makita and Festool cordless tools.
Festool built a partly interlocking system around 27 and 36 millimetres, which is why Festool hoses step and taper to fit both their tools and other machines.
Common collector sizes
Dust collectors and the machines they serve use 4 inch as the near-universal main size, with 2.5 inch as a common branch to smaller tools and 5 inch or 6 inch on larger machines. In metric, 100 millimetres stands in for 4 inch, and because 4 inch is about 101.6 millimetres, the two are close but not identical, which is why some metric and imperial parts are a slightly loose or tight push fit.
The takeaway is that 4 inch and 100 millimetre are treated as interchangeable in practice but are not the same measurement, so a snug seal sometimes needs a wrap of tape or a proper adapter.
Why sizes are nominal
Many dust fittings quote a nominal size that is not the exact measured diameter, and inner versus outer diameter is frequently unstated. A port called 2.5 inch may measure slightly over or under, and a hose slips over or inside a port depending on which diameter is meant. This is why measuring the actual diameter, and noting whether it is the inner or outer, is the reliable way to match parts.
| Nominal size | System | Typical tools |
|---|---|---|
| 1.25 in | Shop vac | Small sanders, detail tools |
| 2.5 in | Shop vac | Sanders, routers, small saws |
| 27 mm | Metric tool port | Festool and cordless sanders |
| 35 mm | Metric tool port | DeWalt, Bosch, Makita tools |
| 4 in / 100 mm | Collector | Table saws, planers, machines |
Sizes are nominal; 4 inch (about 101.6 mm) and 100 mm are close but not identical.
Match your tool port to a hose
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Sources: Festool dust extraction system documentation ยท Oneida Air Systems ducting reference