Bit set comes complete with the most common sizes: T4 T5 T6 T7 T8 T9 T10 T15 T20 T25. Sizes T4, T5 and T6 are too small for us to put a hole in the tip, so only the larger sizes are tamper resistant. Sizes T7 T8 T9 T10 T15 T20 T25 are Tamper Resistant, meaning that they have a hole in the tip to bypass the post that is found in some security screws. But even the tamper resistant bits can be used on regular screws. Made from High Quality CRV6150 steel, these will resist stripping and deforming more than lower quality "Heated", "Treated" or "Carbon" steel. Please make sure you use the correct size, as using the wrong size increases the chances of stripping significantly.