Both tank holders are made of heavy duty, waterproof black nylon. The holder designed to fit M6 size oxygen tanks has convenient double pockets to hold two canisters or a canister, extra tubing, masks, etc. Easily adjusts to fit most wheelchairs. The holder for Size D & E oxygen tanks fit into this holder with minimum lifting and positioning. This holder is designed to position a 26" long tank off-center behind the wheelchair back to avoid interference with the wheelchair user's head or back.