What is a Neck Finish?
A neck finish comprises all the design features located at the neck portion of a bottle or jar that enable the cap to be screwed on or sealed. This structure ensures mechanical compatibility and leak-tightness between the bottle and the cap.
Technical Components of a Neck Finish
A neck finish typically consists of the following elements:
a. Outer Diameter
This is the external diameter of the bottle or jar’s opening. This diameter must exactly match the diameter of the cap to be used.
Unit of measurement: mm
b. Thread Count
This refers to the number of threads that allow the cap to be closed by twisting. It is typically single-start or multi-start.
- Single start: Makes a 360° turn per rotation.
- Multiple start: Allows faster closure (can close in half a turn).
c. Thread Profile
This is the shape and angle of the threads. It is generally determined according to standards.
Example: SPI (Society of Plastics Industry) thread profiles are common.
d. Finish Height
This is the vertical length from the base of the bottle opening to the top surface. It determines how deeply the cap will sit.
e. Bead or Collar
This is a protrusion at the neck that ensures a tight fit for the gasket inside the cap. It is particularly important for sealing.
f. Tamper Evident Band Area
In some neck finishes, there is a special groove or protrusion for a tamper-evident band located at the lower part of the cap. This system, which shows if the cap has been opened, is often used in the beverage industry.
Neck Finish Coding System: SPI Standard (Common in Food and Cosmetics Industry)
Code Format: Diameter (mm) / Finish code
Example: 28/410
- 28: Outer diameter of the bottle opening (28 mm)
- 410: SPI code referring to the neck finish height and thread profile
- Codes like 400, 410, 415, 425, and 430 indicate the height and thread structure.
| SPI Code | Description |
|---|---|
| 400 | Standard short neck, single-thread |
| 410 | Longer neck, suitable for cosmetic pumps |
| 415 | For thin-walled caps |
| 425 | Neck stucture suitable for tamper-evident bands |
Important Neck Finish Types (According to Application Areas)
| Neck Finish Type | Application Area | Description |
|---|---|---|
| 28/410 | Shampoo, liquid soap | For pumps and flip-top caps |
| 38/400 | Food (juice, milk) | Leak-proof caps, tamper-evident |
| 18/415 | Perfume, serum | For fine mist sprayers |
| 63/400 | Jars, sauces | Wide-mouth caps |
| Twist-Off | Jam, pickles, tomato paste | Commonly used for glass jars |
| Snap-on | Baby foods | Push-pull caps |
Industry Standards
- PET Bottle Production: Commonly uses PCO (Plastic Closure Only) codes
Examples: PCO 1810, PCO 1881 (carbonated drink bottles) - Glass Packaging: Uses twist-off or special metal caps
- Cosmetics Industry: Common sizes include 20/410, 24/410, and 28/410
Neck Finish Measurement Methods
Technical drawings include the following values for measurement:
- T (Outer Diameter): Outside diameter of the opening
- E (Thread Root Diameter): Diameter at the root of the threads
- H (Finish Height): Neck height
- S (Thread Start Height): Starting point of the first thread
- I (Inner Diameter): Internal mouth diameter
Why is it Important?
- Incorrect neck finish = Cap incompatibility
- Leakage, customer complaints, manufacturing errors
- Standardization is vital in high-volume production
- Correct neck finish compatibility is mandatory for international sales