These hair trimmer replacement blades are made of metal material, which feature corrosion-resistant and wear-resistant, suitable for long-life use and can stay pointed, sturdy and to be applied for a long timeEach piece of hair clipper replacement blade is designed with 2 holes, which makes it considerate and convenient to operate, brings you cleaner and more stable hair cutting experience, also be applied smoothly to gild through most hair types with ease adjustable hair clippers blades are compatible with 8148, , 8591, 8504, 2241 and 2240, you can just replace the blades according to your needs, and no need to a new clipper, with installation, it can work as effectively as a new oneMake the adjustable lever of the blade go to the full forward position, place the small top blade over the clipper drive finger, then place the bottom blade on top of small top blade, use screws and partially tighten, keep that the extreme left hand tooth of top blade is aligned to the first small tooth of bottom blade, then you can tighten screws, you can switch several to make whether you have aligned blades; Note: the screws are not includedcolour: blackMaterial: metalPackage Contents: 1*big knife1*small knifeOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.