It depends on where you measure them. There seem to be two conventions - one measuring the outside of the speaker frame (5.25") and one measuring across the midpoint of the surround (4-ish). Axiom uses the first method IIRC.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8