Gillott 303 Nib
One of the most popular nibs for copperplate. Good flexibility - not too stiff, not too flexible. Very thin hairlines and good swells. Works for scripts 3/16-1/16". Sharp point, but will work on slightly textured surfaces. Tends to catch on upstrokes.
Mentioned by Eleanor Winters in her Mastering Copperplate Calligraphy. Satisfactory for Spencerian Script.
Price is for one nib.