Getting the Right Fit From Your Closure
Making a closure achieve a good fit to its bottle is extremely important. There are two specific neck finish dimensions of the bottle to keep in mind on the technical side. The H dimension, which is measured from the top of the bottles neck finish down to the shoulder of the bottle and the T dimension, which is the width of the neck finish from outer thread to outer thread (click here to see what we're talking about). There are three general neck finish sizes: 400, 410, and 415. Each of these finishes have there own distinct H dimension so closure manufacturers can make the component fit properly to the bottle, at least they should fir properly.
The Society of the Plastics Industry (SPI) has determined the dimensions of the container and closure for standardized production. However, you will not always get the perfect fit, quality problems do occur. It could be the neck finish of the bottle is not up to standards, or maybe it's the closure. You could run into an issues where the cap bottoms out on the shoulder of the container before achieving a full seal. To be sure you do not run into problems, do your research. Ask for product drawings and samples. Make sure you check that all of the components are compatible before you move into full scale production.