Grodan Stonewool Gro-Blocks Delta 10 - W/ Hole - 4" x 4" x 4" - Known for its quality, consistency and ease of use, high-performance Grodan stonewool is used by hydroponics gardeners the world over. Seeds or cuttings are started in these large Grodan Gro-Blocks and, once rooted, the blocks are transferred to a larger stonewool slab. Gro-Blocks can also be planted directly into containers for soil gardening. This is a strip of six 4" x 4" x 4" Gro-Blocks, each with pre-formed holes. Holes are perfect size for any 1.5 starter plug.