oh yeah that would be an absolute doddle to make with openscad.

The stepping might not be necessary, in which case you're looking at 'funnel' with a few bits tacked on.
Take a picture of the thing it fits to.

One of the best bits about 3d printing is that you can simplify and improve on designs to make them faster and or easier to print.
What makes sense for an injection moulded part - often doesn't make sense for a 3d printed part that does the exact same job.
The stepping is not screw thread i think it's just there to save plastic on a moulding.
Or not, have to see the fitting to know for sure :-)

So things you'd need to measure - mand with digital calipers NOT a fixed rule: https://www.amazon.co.uk/Adoric-Vern...4541864&sr=8-5

worth checking your local lidl - they had them a short while ago for about the same price.

So you need to measure: thicjness of the walls, height, precise size and shape and thickness of the lugs. Angle they are attached to the part.
And yes it does need to be down to 100ths of a mm.
3d printers can be incredibly precise and injection moulded parts are almost never made with whole number measurements.