12 round holes, 5/32" (4mm) in diameter. Possible spacings (depending on seeder sprocket combination) from 1-5" apart. Seed rollers have slots or holes to cup seeds, allowing accurate singulation of very small to medium size raw seeds or pelleted seeds, and are compatible with even some larger seeds. Made of a special anti-abrasion plastic to prevent build-up of static electricity. Trial data: Will singulate the following raw-seeded varieties: Caraflex (cabbage); Rhazes (lettuce); Vit (mache); *Gold Coin, *Bianca Di Maggio, *Redwing, *Red Bull, *Patterson, *Bridger, *Cortland, *Gunnison, *Candy, *Pumba, *Copra, and *Purplette (onion); Cherriette, Rudolf, Crunchy Royale, Easter Egg, D'Avignon, and Rover (radish); Saffron, Picador, and Conservor (shallot); and Shunkyo Semi-Long (specialty radish). Compatible with but won't singulate the following raw-seeded varitieties: White Spear (bunching onion); Skyphos, Panisse, Breen, Five-Star Greenhouse Mix, Mottistone, Green Forest, Salad Bowl, Rouge D'Hiver, All Lettuce Mix, Allstar Gourmet Lettuce Mix, Adriana, Encore Lettuce Mix, Oscarde, Tropicana, Ridgeline, Red Cash, Green Star, Bambi, Flashy Trout Back, Cherokee, Teide, Australe, Wildfire Lettuce Mix, Red Cross, Firecracker, Jericho, Nevada, Winter Density, and Vulcan (lettuce); and Picador (shallot). *Remove felt spring for best results with these varieties.