These nibs are not standard size, they are only compatible with Hongdian forest fountain pen 1850, 1851, M2, 1843, 6013, 517D, 517S, 525,H1, H3, A3, 1843 and 920 Series. Hongdian forest fountain pen (1850,1851), M2, 1843, 6013, 517D, 517S, 525,H1, H3, A3, and 920 Series.