Whether starting your seeds and cuttings in A-OK Starters, Macroplugs, or Mini-Blocks it is a good idea to transplant into a 3” or 4” block. You know it’s time to transplant to the Gro-Block when roots coming out of the starter are about 1” long. Just place your Mini-Block on top of the 3” or 4” block without the hole, or your Macroplug/A-OK into the 3” or 4” block with the hole and watch your plant flourish. Detailed description - Gro-Blocks : Delta 6.5 Small 4" - Sizes in inches : 4x4x2½ - Hole sizes available : Big hole - Blocks/Package : 6 - Blocks/Case : 216