Each row is a real component with the detail the calculation needs: the teeth of every sprocket, the chainrings or the internal ratios. The Load button puts it into the calculator, and from there you can compare it, watch it spin and run it through the climb test. If what you are after is not there, you add it yourself and can take it away in a file.
The cassette does not screw onto the wheel: it slides onto a splined body that is part of the hub, and each manufacturer has its own. If the body is not the one the cassette needs, it will not fit and no adapter solves it: you change the body or you change the wheel.
The two-letter tag next to the brand is the company's country. The data comes from manufacturer catalogues, and every entry carries its source and the date it was checked: you can consult that in the API. Entries that could not be verified are flagged as unreliable rather than hidden.
Data compiled from manufacturer catalogues. Tooth combinations and internal ratios can vary between series and years: always check your component's own spec sheet before buying anything. What is not calculated here is compatibility: derailleur capacity, largest sprocket allowed and chain length. Always check with the manufacturer before buying.
The link holds the whole configuration: bookmark it or send it to anyone.