All of tire chains and tensioners are sold as a pair.
A pair is like a pair of shoes. One for left and one for the right side. 2 pieces. A pair of tire chains cover all tires on that axle. Unless you want to cover all the tires on a vehicle, one pair covers both tires on an axle. For dual tire trucks with 4 tires on an axle, one pair of tire chains covers all 4 tires on that axle.