Plasplugs® Solid Wall Super Grips™ are suitable for fixing into concrete and brick. They are available in 3 different sizes/colours. Yellow: Regular-duty, accepts screws No.4-8 (3-4.5mm)Red: Regular-duty, accepts screws No.6-12 (3.5-5.5mm)Brown: Heavy-duty, accepts screws No.8-14 (4.5-7mm)