Printables link. Apologies for the... very lazy select + background blur. In the land of windows I would have used paint.net, but I'm coming to you from a mac today and haven't found a great alternative.
For this particular project, finding a model that already had the threads in it.
More broadly, threads usually follow one of a handful of standards. It's just a matter of figuring out which standard is being used and then finding the size. I haven't found a great way of approaching that for bigger threads, beyond measure with a pair of calipers, but if you're working on nuts and bolts a metal fixture with various threads is the way to go IMO.