# PET bottle necks: PCO 1881 (soda, 28 mm) and 38 mm (milk/juice)

> What is the thread size of a soda bottle cap?

- Category: Hardware › Found & household materials
- Kind: Standard part
- Basis: PCO 1881 (ISBT) neck finish; 38 mm three-start finish per ISBT; bottle body sizes typical
- Page: https://xemstudio.com/objects/pet-bottle-necks-pco1881/ · JSON: https://xemstudio.com/api/geometry?object=pet-bottle-necks-pco1881 · Plain text: https://xemstudio.com/objects/pet-bottle-necks-pco1881/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Soda / water bottle neck (PCO 1881): thread OD 27.43 mm, thread root 24.94 mm, 2 mm pitch single-start with 3 thread turns, neck height 17 mm from the support ring to the top, support ring Ø33 mm. Cap ID 28 mm. The older PCO 1810 is 21 mm tall with the same thread.
- Milk / juice bottles: 38 mm finish (thread OD 37.5 mm, 3-start, 1.8 mm pitch, 10 mm tall). Water-cooler jugs are 55 mm.
- Bottle bodies: 500 mL Ø65 × 200 mm; 1 L Ø80 × 270; 2 L Ø110 × 310, PET wall 0.3 mm. A printed PCO 1881 cap (thread modeled as a 27.9 mm bore with a 2 mm pitch groove) screws onto any soda bottle: pressure vessel to ~8 bar, the clear cylinder of a water-rocket or a pressure test rig. Never heat PET above 70 °C.

## Sizes

| finish | thread_od_mm | root_mm | pitch_mm | height_mm | cap_id_mm |
|---|---|---|---|---|---|
| PCO 1881 (soda, 28 mm) | 27.43 | 24.94 | 2.0 | 17.0 | 28.0 |
| PCO 1810 (older 28 mm) | 27.43 | 24.94 | 2.0 | 21.0 | 28.0 |
| 38 mm 3-start (milk/juice) | 37.5 | 34.0 | 1.8 | 10.0 | 38.0 |

## Where the files are

- Wikipedia: [Plastic bottle](https://en.wikipedia.org/wiki/Plastic_bottle) — web — CC BY-SA 4.0 (text)
- ISBT: [PCO 1881 finish drawing (International Society of Beverage Technologists)](https://www.threadspecs.com/) — PDF — ISBT publication (verify at link)
- Long Earth Society: [Engine builds (videos and write-ups)](https://longearthsociety.com/engineering/) — web, video — LES site

## Questions

**What is the thread size on a soda bottle?**

PCO 1881: 27.43 mm thread OD, 2 mm pitch, 17 mm tall neck; caps are 28 mm. All standard soda and water bottles use it.

**Can I 3D print a cap for a soda bottle?**

Yes: a 27.9 mm bore with a 2 mm pitch, 1.2 mm deep groove, 3 turns; print at 0.12 mm layers and it seals with a 1 mm silicone disc.

## Fits with

- [Mason jars: regular (70 mm) and wide-mouth (86 mm), half-pint to half-gallon](https://xemstudio.com/objects/mason-jars-and-lids/)
- [Laboratory rubber stoppers #0–#13 and wine corks](https://xemstudio.com/objects/rubber-stoppers-and-corks/)
- [O-rings, common metric sizes (ISO 3601)](https://xemstudio.com/objects/o-rings-metric/)
- [Can-engine printed kit: can caps, diaphragm clamps, displacer guides, crank stands, CD/platter hubs, syringe cradles](https://xemstudio.com/objects/can-engine-printed-kit/)