13.8mm internal diameter circlips as used in the vast majority of door handles.  These circlips are the 'external' type, so-called because they fit on the outside of a shaft.  External circlip pliers should be used to remove and replace them before and after replacing the spring.

13.8mm internal diameter, 1mm thick.  Fit a 14.3mm diameter groove machined into a 15mm diameter shaft.