Doctor Blades for the following cartridges:HP 504A, 504X - CE250A, CE250X, CE251A, CE252A, CE253A HP 507A, 507X - CE400A, CE400X, CE401A, CE402A, CE403A HP 647A, 648A, 649X - CE260A, CE260X, CE261A, CE262A, CE263A .Sold in 10 packs only. Compatible laser printers:HP 504A, 504X - HP CP3520, CP3525, CM3530.HP 507A, 507X - HP Enterprise 500, M551.HP 647A, 649X - HP CP4520, CP4525, CM4540.