The main difference between Pen and Pin is that the Pen is a writing implement and Pin is a fastening device; device used for fastening objects or material together; often has two components: a long body and sharp tip made of steel, or occasionally copper or brass, and a larger head often made of plastic.

As nouns the difference between pen and pin is that pen is an enclosed area used to contain domesticated animals, especially sheep or cattle or pen can be a tool, originally made from a feather but now usually a small tubular instrument, containing ink used to write or make marks or pen can be a female swan or pen can be penalty while pin is a small device, made (usually) of drawn-out steel wire with one end sharpened and the...