75 mm (3 Inch) Magnetic Compass or Travel Compass or Military Magnetic Compass Ideal for locating positions on a map or in the field. Compasses are a navigational instrument designed with the Earth’s magnetic field. They generally use a needle to indicate the direction of North, and prove to be invaluable when in the wilderness or out at sea. Large Font Size, Easy to Read. Excellent for hiking, camping and outdoor activities. Inner Diameter. Material: Mainly Metal. Made in China. This is the best quality and standard size magnetic compass.