Will 0.9 lead fit in pencils that use 0.7?

No, a 0.9 mm lead will not fit in pencils designed for 0.7 mm lead. The diameter of the lead is different, and the pencil's mechanism is specifically tailored to accommodate the size of the lead it is designed for. Attempting to use 0.9 mm lead in a 0.7 mm pencil could lead to jams or damage to the pencil.