These are standard '130 size' DC hobby motors. They come with a wider operating range than most toy motors: from 4.5 to 9VDC instead of 1.5-4.5V. This range makes them perfect for controlling with Arduino where you are more likely to have 5 or 9V available than a high current 3V setting. They'll fit in most electronics that already have 130-size motors installed and there's two breadboard-friendly. This Toy motor is cheapest in India.