Adapter

An adapter is a part which allows to place multiple stacks of parts below a single stack. With version 0.21 there are six different types, where half of them have one small and the other half one large node on the top and for each top size are either two, three or four outgoing connections for small sized parts.

The propellants liquid fuel and oxidizer will flow through it. The branches are unsupported and prone to bending or breaking if the weight and thrust are not properly distributed. Rockets incorporating an adapter are also likely to wobble, unless the stacks are opportunely bound together with EAS-4 Strut Connectors.

Another, unconventional use of those parts is as a landing 'foot' - when landing very large craft (such as bases), the stock landing legs aren't big or powerful - using the strut parts as 'legs' and the tricoupler as a 'foot', it can artificially make its own landing leg!