Basic prong training collar is used to imitate the sensation of another dogs teeth in a correction. It's a comforting familiar communication a dog understands. All dogs should be trained in these collars they just work without damaging a dogs neck. Flat collars cut off a dogs throat and can cause serious damage. Regular slip chains and martingales create pressure on one point leading to un-precise or confusing communication.prong collars evenly distribute pressure and give a clear signal. You cannot damage the dog if collar is used as responsible training tool. Not meant for the out or permanent wear. Most dogs can use small size add links to increase diameter small is 16" spare links sold in packs of 3.