The Speed Feed Blades fit the 305 model Speed Feed Trimmer handpiece and the NEW Cat trimmer "Purrl". Interchangeable with steel or ceramic blades. Choose your favorite type when purchasing. All will work on your trimmer. Some blade sizes may be available in only ceramic or only steel. Ceramic helps reduce friction and any heat as well as stay sharper much longer. Your dollar goes further. The ceramic blade has white cutter teeth. Steel is economical and slightly less fragile than the ceramic. The steel blade has black or gray cutter teeth.