Designed for General Drilling Purpose in Relatively Soft Materials These metric drill bits are made of high-speed steel 4241. There are several commonly-used HSS types: 4241, 4341, M2, M35, M42. HSS 4241 is of the lowest price and relatively lower quality compared to others. The material decides that they can be used mainly in drilling wood, plastic and soft metal sheet like aluminum. If your purpose is to drilling metals, please buy our M35 grade drill bits. Both metric and fractional inch sizes are available.Titanium Coating There are two types of titanium coatings: industrial coating and decorative coating. The former one is quite expensive and only used on premium materials like M35 and M42. The finish of this bit set is decorative titanium coating, mainly for anti-rust and decoration.Package and Size Label This bit set are packed in a light, tough and transparent PVC index case. The size labels are printed on the bit holder and engraved on the shanks of bits larger than 3mm in diameter.About Size Error You may have noticed some negative reviews about size. The results vary due to different tool and different measuring ways. Please refer the last picture for right measuring method. One better way to decide a bit's size is to drill a hole and measure the hole. Then you'll find that the size error of our product is quite small.Responsive and Helpful Customer-service Team If you have any pre-sale, after-sale question, please remember our customer-service team will respond to your email within 12 hours.