The most common reason a dust collection adapter does not fit is a wrong measurement. Either the customer measured the inner diameter when the adapter needs the outer, or they measured across the threads instead of the smooth part of the stub.
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 stub. This is what the adapter grips.
When you put an adapter over a port (the adapter slides onto the outside of the stub), you need the outer diameter. When you push an adapter into a port (the adapter goes inside a hose or opening), you need the inner diameter.
GulpDust adapters slide over the tool's port stub. So we list port sizes by outer diameter (OD).
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 stub.
- Close the outer jaws (the big jaws at the top) around the outside of the port stub. The jaws should be perpendicular to the port axis, not at an angle.
- Read the measurement. This is your outer diameter.
- Open the inner jaws (the small jaws at the bottom) and measure the inside of the port opening. This is your inner diameter.
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
| What You Measure | What It Means | Brand(s) |
|---|---|---|
| OD: ~27mm | Festool 27mm standard | Festool all tools |
| OD: ~32mm | Milwaukee/DeWalt/Ryobi standard | Milwaukee M18, DeWalt 20V, Ryobi ONE+ |
| OD: ~35mm | Bosch/Metabo HPT standard | Bosch 18V, Metabo HPT |
| OD: ~36mm | Makita LXT/XGT standard | Makita all platforms |
| OD: ~47.6mm | 1-7/8 inch shop vac hose | Most US shop vacs |
| OD: ~63.5mm | 2-1/2 inch duct/shop vac | Large vacs, miter saws, table saws |
| OD: ~101mm | 4-inch dust collector duct | Cabinet saws, dust collectors |
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. Port stubs 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 stub. The port may be slightly oval or tapered. Take the larger of the two readings to ensure the adapter fits over it.
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 OD for most major tools already in our database. Select your tool, then select your vac, and we match the adapter automatically.