0.25mm is larger diameter than 0.18mm. Larger diameter is ideal for skin that is thicker such as ethnic skins.
These are Flexi Blades meaning they are not Hard Blades. The differences between Flexi vs. Hard blades is that Flexi blades provides manuveribility and less traumatized for the skin.
Types: Flexi blades for Microblading
Number of Needles: 14 Pins, 16 Pins, 12U
Usage: for all skin types
Proper sterilized Gamma Rays
For thin to normal skin: normal pressure
For thick skin: slightly more pressure.