The Rockwool Hydroponics top cover has 1-inch square holes punched most commonly on 8-inch centers. There is no need to spend hours punching or drilling holes in the lids because they come pre-punched with 1"square hole on 8" centers, or another spacing of the grower's preference (custom punches are available with any order over 350 pieces). These punches as the channel depth are the perfect size to accept a 1" square of Grodan rockwool cubes, Oasis, and many peat/coir cubes. For 8' channels, two 4' top caps each containing six holes are needed. For a 10' channel you will need one 5' top cover with 7 holes and one 5' top cover with 8 holes. 12' channels will require three 4' top caps with six holes each. Find NFT hydroponic materials below.