< Back to Articles

How do I know how to calculate a cap & neck size?

Cap and Neck Finishes

Screw thread cap sizes are generally expressed as two numbers. The first number refers to the cap diameter (in millimeters) and the corresponding Glass Packaging Institute (GPI)/Society of the Plastics Industry (SPI) finish diameter. The second number refers to the height and thread configuration of the closure or finish. The following is a selection of commonly used caps and finishes:

Cap & Neck Finishes

Neck Finish Dimensions

"I" Dimension
The inner diameter of the bottle neck. Specifications require a minimum "I" to allow sufficient clearance for filling tubes. Liner-less closures, with a plug or land seal, and dispensing plugs and fitments require a controlled "I" dimension for a proper fit.

"T" Dimension
The outside diameter of the thread. The tolerance range of the "T" dimension will determine the fit between bottle and closure.

"E" Dimension
The outside diameter of the neck. The difference between the "E" and "T" dimensions, divided by two, determines the thread depth.

"H" Dimension
The height of the neck finish. Measured from the top of the neck to the point where the diameter "T", extended down, intersects the shoulder.

"S" Dimension
Measured from the top of the finish to the top edge of the first thread. The "S" dimension is the key factor which determines the orientation of the closure to the bottle and the amount of thread engagement between the bottle and cap.

Cap Dimensions

Neck Thread Dimensions

MM T min max E min max 400H min max 410H min max 415H min max S min max I
13 .514 .502 .454 .442 - - - - .457 .437 .052.022 .218
15 .581.569 .521.509 - - - - .572 .542 .052.022 .258
18 .704.688 .620.604 .385 .355 .536 .508 .632 .602 .052.022 .325
20 .783.767 .699.683 .386.356 .569 .539 .757.727 .052.022 .404
22 .862.846 .778.762 .386.356 .600 .570 .852.822 .052.022 .483
24 .940.924 .856.840 .415.385 .661631 .972 .942 .061.031 .516
28 1.088 1.058 .994.974 .415.385 .723.693 1.0971.067 .061.031 .614
30 1.127 1.107 1.033 1.013 .418.388 - - - - .061.031 .653
33 1.265 1.241 1.171 1.147 .418.388 - - 1.289 1.259 .061.031 .791
35 1.364 1.340 1.270 1.246 .418.388 - - - - .061.031 .875
38 1.476 1.452 1.382 1.358 .418.388 - - - - .061.031 .987
40 1.580 1.550 1.486 1.456 .418.388 - - - - 061.031 1.091
43 1.654 1.624 1.560 1.530 .418.388 - - - - .061.031 1.165
45 1.740 1.710 1.646 1.616 .418.388 - - - - .061.031 1.251
48 1.870 1.840 1.776 1.746 .418.388 - - - - .061.031 1.381
51 1.968 1.933 1.874 1.839 .423.393 - - - - .061.031 1.479
53 2.067 2.032 1.973 1.938 .423.393 - - - - .061.031 1.578
58 2.224 2.189 2.130 2.095 .423.393 - - - - .061.031 1.735
60 2.342 2.307 2.246 2.213 .423.393 - - - - .061.031 1.883
63 2.461 2.426 2.367 2.332 .423.393 - - - - .061.031 1.972
65 2.579 2.544 2.485 2.450 .423.393 - - - - 061.031 2.090
70 2.736 2.701 2.642 2.607 .423.393 - - - - .061.031 2.247
75 2.913 2.878 2.819 2.784 .423.393 - - - - 061.031 2.424
77 3.035 3.000 2.941 2.906 .502.472 - - - - .075.045 2.546
83 3.268 3.233 3.148 3.113 .502.472 - - - - .075.045 2.753
89 3.511 3.476 3.391 3.356 .550.520 - - - - 075.045 2.915
100 3.397 3.902 3.817 3.782 .612.582 - - - - 075.045 3.344
110 4.331 4.296 4.211 4.176 .612.582 - - - - 075.045 3.737
120 4.724 4.689 4.604 4.569 .700 .670 - - - - 075.045 4.131

Threads Per Inch

MM Thread/Inch
13 12
15 12
18 8
20 8
22 8
24 8
28 6
30 6
33 6
35 6
38 6
40 6
43 6
45 6
48 6
51 6
53 6
58 6
60 6
63 6
65 6
70 6
75 6
77 6
83 5
89 5
100 5
110 5
120 5
Title: How do I know how to calculate a cap & neck size?
Description: A brief explanation on understanding the cap & neck finish on bottles.
Published: 7/21/2003
Last Edited: 4/15/2019
76 users found this article useful. Was this article useful to you?
Share

Information disclaimer:

The information contained in this article is for general information purposes only. The information is provided by United States Plastic Corp. and while we endeavor to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.

In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from loss of materials, time or profits arising out of, or in connection with, the use of this information.