Grodan 1.5"  inch Rockwool PRO A-OK Starter Plugs (98/sheet) (30 sheets/case) A-OK Starter Plugs are used to propagate both seeds and cuttings. Each plug measures 1.5" x 1.5" square and comes unwrapped on a sheet of 98 which is designed to fit into a 10" x 20" nursery flat. These come 30 to a case.