Drainage Gravel 5-7mmOur drainage gravel consists of crushed blue metal screened from 5mm to 7mm in size. Blue metal drainage gravel is suitable for using for filling trenches, around pipes (the most common application for this sizing) and drainage and for other drainage purposes. Due to its sizing, this stone is also known as pea gravel. This gravel can also be used as a cost effective solution in landscaping design. Drainage Gravel Benefits Durable and resistant to