Features:You do need to initially fill your jar to the top with the desired product to create the vacuum.When the pump is pressed a piston on the bottom of the container will push the product upward and out of the top.------------------------------------------------------------Specifications:15ml: approx.5.2 x 6cm / 2.05 x 2.36''30ml: approx.5.2 x 7cm / 2.05 x 2.76''50ml: approx.6.2 x 7.3cm / 2.44 x 2.87''These pumps use a vacuum action instead of a straw so you can use every drop of your product.