A piston and scraper assembly (26) for a high-pressure liquid chromatography column (1) is provided with a snap lock between the piston (5) and the scraper (25). The snap lock comprises a groove (23) in the piston wall (17), a complementary groove (39) in the inner face of the scraper (25) and a locking, sealing and biasing means such as a resilient O-ring (43) which fits into said grooves.