Making a closure achieve a good fit to the bottle has a lot to do with one dimension, the H. The H dimension is measured from the top of the bottle finish to down to the shoulder of the bottle using a line drawn parallel to the T dimension (the width of the finish from outer thread to outer thread). The SPI finish sizes 400, 410 and 415 each have a distinct H dimension to be made to so that closure manufacturers can make their component to fit properly onto these size bottle finishes.

Suppose you are specifying a 24mm closure for a 24-410 bottle finish. You get samples or a drawing of the component from a supplier and the supplier tells them this is our 24-410 closure and it should work great. Next thing you know, there are closures that are bottoming out on the shoulder and everyone is unhappy. How could this occur? Aren’t all 24-410 closures and bottles the same? Well if the bottle is not made to SPI standards for a 410 series neck, it could be an issue. Sometimes manufacturers make bottles with a custom H so that it will accommodate a custom closure for a different customer. If that is not known at the time of specifying all the components, that could easily cause problems down the road. Or the closure may be a custom design and not follow the standards that are set by Closure Manufacturers Association. This is why it is always a good idea to have the drawings of the two components reviewed prior to the start of a project so that so that everything is in order as of the first component order.