Micro rings aka easy ring extensions are a very popular method in hair extensions. They are very small (approx 4mm) metal rings, coloured in either black, brown, dark brown or blonde to match your hair colour.
The application will see a strand of hair extension clamped tightly inside the ring along with your natural hair. This is a very durable method of hair extension application.
These can last you between 3-5 months, and would require maintenance every 6 weeks depending on your hair growth and maintenance.