I’ve been playing harp since January. I have a Stoney End Evensong harp with sharping levers on the C, F, and B strings. That combination appears to be fairly common — I notice that the ads for other harps talk about C, F and B levers as well (the info for Flatsicles says that that lets it handle C, G, D and F and the relative minors).
However, I’m puzzled (and this may sound silly) — I know that the key of C uses no levers and that G uses the F lever and D uses the F and C levers. But what’s the B lever do? It sharpens B, so that doesn’t seem to be the way to make a Bb needed for the key of F….