Cartridges feature accurate flow rates and adjustable tubing retainers to hold tubing in place ¿ for large cartridges, set tubing retainers to your tube size and you are ready to pump. On small cartridges, optimum retention is preset ¿ simply load tubing and start pumping. Cartridges are constructed from polycarbonate and glass-filled nylon. Mix small and large cartridges on pump heads that accept both sizes; two small cartridges occupy the same space as one large cartridge.