There are a number of points to consider when selecting a liner. The first is to ensure that the overall liner dimensions are compatible with your injector.  For convenience, liners in our catalog are grouped by instrument manufacturer. 

Secondly, the liner must have sufficient volume to contain the vapor created by the injection, so the liquid volume and expansion volume of the solvent injected must be considered.

Finally, the injection technique used must also be considered. For example, if conducting split injections, then due to the high gas flow through the liner you will probably be fine with a 4mm ID liner. If doing splitless injection, you may consider using a low volume liner (i.e. 2mm ID) to minimize band broadening in the liner.