The neck finish is the rim at the top of a glass bottle, threaded or smooth, where the closure attaches, and it decides which closures will fit. It is formed with the glass and cannot be altered afterwards: a bottle made with a 28 mm thread will never take a 30 mm cap. Choose the closure first, then confirm the full finish code against it before ordering bottles.
How to read a finish code
A finish covers three things: the thread pattern, the opening diameter and the sealing surface. It is written as two numbers, such as 28-400, 24-400, 30-400 or 38-400. The first is the outer diameter in millimeters. The second is a code for the thread pitch or style.
One diameter can come with more than one thread code. Give the closure maker the complete code, never the diameter alone.
Which finish each closure type needs
| Closure | Finish it needs | Typical use | Point to watch |
|---|---|---|---|
| Screw cap | Threaded, from 18 mm on small vials to 53 mm on wide-mouth jars | Food, beverage and cosmetic bottles | Liner must suit the product |
| Dropper | 18mm-style thread: GL18, DIN18 or 18-410 | Essential oil and serum bottles, 5ml to 30ml | Catalog code does not guarantee tolerance |
| ROPP | Smooth or lightly threaded, around 28 mm and 30 mm | Spirits | Applied by machine |
| Crimp | Smooth lip with a ring | Beer and champagne formats | Not resealable |
| Cork | Smooth cork finish, sometimes slightly tapered | Wine and high-end spirits | Cork sized to the mouth |
Screw caps
Screw caps are the most widely used closure on glass. They turn onto a threaded finish, seal against a liner or gasket and open easily. Most perfumes, oils and sauces sit on 20 mm, 24 mm or 28 mm finishes. Because these caps are made in enormous volumes, they are also the easiest closure to move from one supplier to another.
The seal is the practical limit. Thin liquids need a good liner, and a product with a long shelf life needs that liner matched to its formula.
Dropper finishes
European catalogs list the small dropper finish as GL18 or DIN18; US and Asian lines call it 18-410. Since it spans most 5ml to 30ml bottles, a single dropper family can serve an entire product line. Our amber dropper bottle with a euro dropper is a ready-made example of this pairing.
For the customer, the dropper defines the experience more than the bottle does. On a wrong finish it wobbles, leaks or cross-threads during filling. Check the code on a physical sample with the real dropper fitted. If you want a child-resistant or tamper-evident closure, confirm that option exists for the finish before you commit.
ROPP caps
ROPP stands for roll-on pilfer-proof. The cap starts as a plain aluminum shell, and a machine rolls it onto the neck, forming the threads as it goes. A band breaks at first opening and shows tampering, which is why ROPP is standard for spirits in many markets.
Crimp caps
A crimp closure is held by a crimped metal band and put on with a capping machine. It is effectively permanent, so it belongs on single-use formats.
Cork
Cork goes in by hand or by machine. The finish diameter sets the cork size, and a poor match to the bottle mouth causes seepage or a cork that is hard to pull. Natural cork can be porous or crumble, so it is rejected at inspection more often than caps are. Some producers switch to technical or synthetic cork for consistency while keeping the opening ritual.
Confirming the finish before you order
For a custom bottle, work in this order:
- Settle the closure type.
- Send us the closure type and, ideally, the closure supplier's spec sheet, so the finish code can be confirmed with the glass plant. Our custom bottle options show what can be specified.
- Order a sample with the actual closure fitted. A cap that matches on paper can still wobble on glass when tolerances drift.
Stock bottles reverse the logic, because their finish is already fixed. Find out which finishes your chosen bottles offer, then pick closures from that list. For a compatibility check on your target capacity, send us your closure plan.