Unlike other types of connections that require tool calibration or go/no-go gauges, expansion is a completely visual connection. If you can see the expansion ring touching the shoulder of the fitting, it is connected properly. The properties of PEX work with this connection. Due to the shape memory of PEX, the weakest that this connection will ever be is when it is first joined. As the PEX contracts, it will increase the strength of the connection. The fittings have virtually the same inside diameter as the pipe, creating less restriction and often allowing for smaller pipe sizes. It also makes the connection impossible to dry-fit. The tools are close to one size fits all, with the exception of the expansion heads, which need to be changed out for different pipe sizes.
