These hose adapters REALLY SUCK!!!
This is a spreadsheet parameterized Freecad 0.18 file for generating printable adapters/couplers for vacuum hoses and accessories. It can make them in any size and gender, as long as it is a straight with tapered connections on either end. The 'aero styled' transition areas minimizes the chances of debris getting snagged on the adapters. They also give lower air drag than the usual ruler sketched adapters.
If you're not familiar with Freecad, generating a custom stl is an easy 3 step process once you have the file opened... from the right side tree view panel, 1- double click the "data" spreadsheet and change the values as needed (use the uploaded image for reference), 2- choose the kind of adapter you want of the 3 available parts and click on it's "revolution", 3- then do file/export... done.
The included example STL's are roughly sized for 2.5" and 1.25" hoses or accessories.
[Update: Added a version 2 freecad file with some small changes. The 'out-out' model has improved geometry for more secure build plate adhesion. I set the build plate rim to 1mm thickness which should be adequate for most situations (it's not in the spreadsheet, but if you need a wider or narrower 'footprint' just edit the drawing itself). I also the way I defined the 'outside' fit geometries in version 1 could be problematic for some choices of dimensions. So I redefined those geometries to get more consistent and reasonable thickness, and to guarantee a consistent 20degree leading edge.]
Have a look through the Freecad file to see how I designed this. It took me twice as long to draw the dimensions image file and type this posting than it took to draw and parameterize the 3 adapters in Freecad. It's just 3 revolved sketches using some white and blue lines, b-splines, and some spreadsheet references to get it locked in.