What Is a Neck Finish? Understanding 18mm vs 20mm Before You Order
One of the most confusing concepts for first-time cosmetic glass container buyers is the neck finish. This guide explains what "18/415" and "20/410" mean, why they matter, and which accessories are compatible with each.
1. Neck Finish Notation: What the Numbers Mean
Neck finish is expressed in "diameter/thread turn" format.
| Notation | Meaning |
|---|---|
| 18/415 | Neck outer diameter: 18mm |
| 18/415 | 2 thread turns (4=400 series, 15=thread height) |
| 20/410 | Neck outer diameter: 20mm |
| 20/410 | 1.5 thread turns (thicker threads) |
Key point: The first number (18, 20) is the neck opening diameter in mm. The second number (410, 415) indicates thread type. Container and closure must share the same neck finish.
2. 18mm vs 20mm: What Sets Them Apart
A comparison of the two most common neck finishes in cosmetic glass containers.
| Factor | 18mm (18/415) | 20mm (20/410) |
|---|---|---|
| Primary volumes | 15-50ml | 30-100ml |
| Thread turns | 2 turns (finer threads) | 1.5 turns (thicker threads) |
| Typical containers | Serum bottles, small ampoules | Essence bottles, mid-size bottles |
| Closure options | Dropper, small pump, membrane cap | Dropper, mid pump, spray, membrane cap |
| Visual impression | Slim, refined look | Stable, generous look |
Note: 18mm and 20mm closures are NOT interchangeable. When sourcing containers and closures separately, always verify matching neck finishes.
3. Neck Finish Compatibility Matrix by Accessory
Once you have selected a container, verify compatible accessories for your neck finish.
| Accessory | 18mm | 20mm |
|---|---|---|
| Metal dropper | O | O |
| Injection dropper | O | O |
| Essence pump | O | O |
| Metal essence pump | O | O |
| Membrane cap | O | O |
| Dropper cap | O | O |
JeongwooCos stocks accessories for both 18mm and 20mm neck finishes, allowing container and closure matching from a single source.
4. Practical Tips for Choosing a Neck Finish
If you are unsure which neck finish to choose, follow these guidelines:
- Volume under 30ml with serum/ampoule formulation: 18mm recommended
- Volume 50ml or above or essence/lotion formulation: 20mm recommended
- If you selected closures first: match your container to the closure neck finish
- MOQ constraints: choose standard neck sizes (18 or 20) to maximize accessory options
Neck finish mismatch is the most common mistake when sourcing containers and closures from different suppliers. Always verify compatibility.
JeongwooCos supplies glass containers in 18mm/20mm standard neck finishes with compatible accessories (droppers, pumps, caps, packing) as a one-stop solution. If neck finishes are confusing, reach out through our Contact page.
