Made by Waterway
This hot tub pipe extender is used to do exactly that, extend pipe, it fits inside the pipe enabling it to be 3cm longer.
2" Hot Tub Pipe Extending Connector Dimensions:
1 end fits inside 2" pipe (5.2cm) and the other fits into a 2" fitting (6cm). The internal of the smaller size is the same as the internal of 2" plumbing which means you can stack these together.