Hi hope your have a class day our airline connectors are pieces of non-toxic plastic that allow you to connect two or more air tubing and more.
You are looking at the multipack of connectors.
Pack contains one of each connector.
X1 elbow
X1 T
X1 straight 
X1 y
connectors can split your air tubing to run a second air stone from the same pump. You can also combine two inputs to create one stronger output for use with multi-outlet pumps.
Work well on standard-sized 4mm upwards air tubing that fits most air pumps.
All connectors Dimension are listed in photos.
Cheers for looking will post as soon as purchased