WARNING: Drilling, sawing, sanding or machining wood products can expose you to wood dust, a substance known to the State of California to cause cancer. Avoid inhaling wood dust or use a dust mask or other safeguards for personal protection. For more information go to www.P65Warnings.ca.gov/wood.
I bought this to connect a shop vacuum to a benchtop narrow belt / disk sander. It worked as advertised. The inclusion of both inside- and outside-diameters in the catalog is what made me choose Rockler over a competitor which left too much to guesswork.
I have some of Jim Byrnes' Model Machines power tools and this adapter fits their tools to a standard shop vacuum. The old adapter from Rockler actually fits better as the long 1-1/2" neck used to be the right length for these tools. But my band saw made short work of cutting this neck down to the right length...no big deal.
This is the second adapter I got for my equipment. The 2 1/2" end fits my band saw and jointer, so I leave them in place and move my Shop Vac to the other end when I need it. Sure cuts down on the dust and shavings.
Inside diameters, outside diameters, and 4" that is not 4"! It is bad enough that there are not universal sizes, but when 4" is actually 3.85", or 4.1", nothing fits anything else. This fits most shop vacs, (though its 2.5' is not...) but the 1.5" side is 1.5" outside diameter and is the same as my miter saw and small oscillating sander, so I had to use a piece of plastic hose to adapt this adapter.