A small piece of non-toxic plastic that allows you to connect two or more breathing circuits. T-connectors can split your breathing circuit to run a second air stone from the same pump. You can also combine two inlets to create a more powerful output for use with multi-outlet pumps. Works well on standard size 5mm ID air tubing which fits most air pumps. air. T -Dimension of the connectors: 3 cm (L) x 1.8 cm (W) x 0.6 cm (T). Dimension of straight connectors: 3 cm (W) x 0.8 cm (D) Package includes 20 T-connectors and 20 straight connectors.