Product, container – piston combination, and whether the syringe or cartridge will be used with a medical device like an injection pen, are the most common factors to consider when deciding which method is best for placing the piston within a syringe. Vacuum piston insertion has the advantage of reducing the air bubbling that is common to the mechanical vent-tube method. This reduction of air bubbles within the syringe eliminates potential oxidation problems with the product and can increase product shelf life. Vacuum can be provided with a mechanical assist, uses a pin to accurately position the piston after vacuum has been pulled. This is commonly done for syringes and cartridges that will be used with medical devices so that they can dispense accurately. Finally, certain silicon free syringes like West Pharmaceuticals CZ syringe require vacuum to be used because of the material mechanical properties of the piston exterior coating. Syringe piston insertion using a mechanical vent-tube approach is good for application using a glass syringe with a bromobutyl stopper, for products with low vacuum pressure and where product oxidation is not a risk.