Seat planks are 10 in. wide with a ribbed no-slip surface. Powder coated planks keeps aluminum from rubbbing off on your clothing. Comes with Safety End Caps-No sharp edges to snag clothing or skin. Frames are constructed of heavy duty commercial grade 2-3/8 in. O.D. galvanized steel. Indoor or Outdoor use - All frames are pre-drilled to be converted to indoor use. Indoor conversion kit can be purchased seperately. Permanent bench with back 21 Feet Long. Bench with backrest. Bench Length: 21 Feet. Seat Plank: 10 in. wide Get ready to enjoy the sunshine with this sleek, 21 foot permanent bench with back! Designed with 10-inch no-slip powder coated aluminum planks, this bench is durable enough for the indoors or outdoors.