The most common reason a dust collection adapter does not fit is a wrong measurement. Some ports are an opening, so you need the inside number. Some are a stub, so you need the outside number. Measuring the wrong one, or measuring across the threads instead of the smooth part, is the usual mistake.
Here is the right way to measure any tool dust port in under two minutes.
Inner Diameter vs. Outer Diameter
Every round port has two relevant measurements:
- Inner diameter (ID): the opening you see looking straight into the port. This is the size of the airflow path.
- Outer diameter (OD): the outside of the port, measured across a stub if your tool has one.
Check the shape of your port first. When a hose or adapter goes over a stub, you need the outer diameter. When a hose or adapter goes into an opening, you need the inner diameter.
GulpDust adapters go into an opening, so we build to the inner diameter (ID) of the port. If your tool has a stub port instead, our adapters today are male on both ends and may not suit it. Ask us before you order.
Tools You Need
Option 1: Digital calipers ($10 to $20). These are the most accurate and fastest option. Any basic set works fine for this purpose.
Option 2: A ruler and a strip of paper. Wrap the paper around the port stub, mark where it overlaps, unroll it, and measure the circumference. Divide by 3.14159 to get the diameter.
Option 3: A set of drill bits or round objects of known size. Try them against the port until you find the closest fit.
How to Measure with Calipers
- Make sure the tool is off and unplugged.
- Open the calipers wider than the port.
- Close the outer jaws (the big jaws at the top) around the outside of the port. The jaws should be perpendicular to the port axis, not at an angle.
- Read the measurement. This is your outer diameter. Use this number if your port is a stub.
- Open the inner jaws (the small jaws at the bottom) and measure the inside of the port opening. This is your inner diameter. Use this number if your port is an opening, since that is what our adapters are built to.
If the port has a slight taper (some ports are wider at the base and narrower at the tip), measure at the midpoint of the stub length.
Common Measurements You Will Find
These are the numbers most people land on. Whether yours is an inside or an outside reading depends on your port shape, so check that first.
| The Number | Where It Lands |
|---|---|
| ~27mm | The 27mm port hub |
| ~32mm | The 1-1/4 in. port hub |
| ~35mm | The 35mm port hub |
| ~36mm | The 36mm port hub |
| ~47.6mm | A 1-7/8 inch shop vac hose, not a tool port |
| ~63.5mm | A 2-1/2 inch duct or shop vac hose |
| ~101mm | A 4-inch dust collector duct |
If You Get a Weird Number
Round to the nearest standard size. If you measure 31.5mm, that is a 32mm port. If you measure 34.8mm, that is a 35mm port. Ports are not precision machined, they vary by 0.5 to 1.0mm from unit to unit.
If you are between two standard sizes (say, 33.5mm), measure again at a different point on the port. The port may be slightly oval or tapered. Take the larger of the two readings so you order the size that will actually go on.
Measuring the Shop Vac Hose
Shop vac hoses have two relevant sizes:
- The hose inner diameter (what the adapter inserts into)
- The cuff outer diameter (the plastic fitting at the end of the hose)
Most US shop vac hoses are 1-7/8 inch (47.6mm) inner diameter. Some smaller vacs use 1-1/4 inch (31.75mm). Large shop vacs (16 gallon and up) often use 2-1/2 inch (63.5mm).
Check the cuff, the plastic part at the end of the hose. It will usually have the hose size molded into the plastic. If not, measure the inner diameter of the cuff opening.
When to Use the Configurator Instead
If you know your tool brand and model number, skip the measuring step and use the GulpDust configurator. We have the port size for most major tools already in our database. Select your tool, then select your vac, and we match the adapter automatically.