Grodan Stonewool Gro-Blocks Delta 4 - NO HOLE - 3" x 3" x 2.5" - Stonewool is recognized the world over as the ideal hydroponics growing substrate. Seeds or cuttings are started in these small Grodan Gro-Blocks and, once rooted, the blocks are transferred to a larger stonewool slab. Gro-Blocks can be planted directly into containers for soil gardening as well. This is a strip of eight 3" x 3" x 2.5" Gro-Blocks, without pre-formed holes. Grodan stonewool is known for its quality, consistency and performance.