The MJ-4 seed roller has four V-shapped holes, 15/64" (6mm) in diameter. Spacing is adjustable from 6-15” apart depending on seeder sprocket combination. Seeder rollers have cups/holes to cup the seeds to allow for singulation. Made from anti-abrasion plastic to prevent build-up of static electricity that causes seeds to stick together. Great for Carrots, Lettuce, Onion.