Cap Buying Guide

Find the Right Size Cap for a Bottle or Jar

thread-finish-closeup.jpgThere are many different types of cap available for plastic and glass jars, and it's a challenge to interpret cap sizes without instruction. If a bottle and a cap do not have the same size/style designation, they will not work together even if they look similar in size.

Below is an overview of how to pick the correct cap for your bottle.

Caps are identified by two numbers with a dash in between, generally written as either 24-400 or 24/400.

When measuring your cap size, the first number refers to the diameter of the bottle neck (not the cap) from the outside thread on one side to the outside thread on the other side, in millimeters.

The second number represents the GPI or SPI* thread design and height of the cap and container.

To determine the thread style or "thread finish" of a bottle or jar, observe the height, and count how many times the threads pass one another. Then compare it to this chart to find the second number, or thread style:

410-thread-finish.jpg  415-thread-finish.jpg  425-thread-finish.jpg  430-thread-finish.jpg   lug-finish.jpg
1 thread turn, common for jars
1.5 thread turns, common for vials
2 thread turns, tall, common for vials
2 thread turns, short, common for vials
Buttress finish
features thick
threads & top bead, common for jugs
Lug finish
features non-continuous threads, common for economy jugs


Some common products that use these sizes:

 Glass Jar with 58-400 finish  15 dram Clear Glass Vial with 24-410 Hole Cap15 dram Clear Glass Vial with 24-410 Hole Cap  10mL Serum Vials, 20-415 thread  4mL Clear Glass Vials, 13-425 Cap 4 Liter LDPE Bottle with 38-430 Cap Dairy jug with lug finish
64oz Dairy Jug, HDPE, Lug finish

*The Glass Packaging Institute (GPI) and Society of the Plastics Industry (SPI) have provided standardized neck finishes for glass and plastic containers.