Neck Finishes Explained: What 24-410 Actually Means
The two-number code on every bottle opening determines which caps will fit — and ordering mismatched components is one of the most expensive mistakes in packaging sourcing. Here's how to read it.
In this guide
What is a neck finish?
A neck finish is the standardized thread profile on the opening of a bottle or jar. It defines the diameter of the opening and the geometry of the threads — so a cap designed for one finish will engage cleanly, torque to the correct foot-pounds, and seal reliably. A cap designed for a different finish won't.
The finish isn't just a thread. It includes the outer diameter of the neck, the thread pitch, the number of thread turns, where the thread starts, and the depth of the thread channel. All of those dimensions are captured in a two-number code — a standard first developed by the Glass Packaging Institute (GPI) and now used across glass and plastic packaging alike.
Every bottle in our catalog lists its neck finish. Every cap listing shows which finishes it fits. Matching those two correctly is the single most important spec check before placing an order.
How to read the numbers
A neck finish code always takes the form NN-TTT — a diameter number, a hyphen, then a three-digit thread style number.
First number — diameter in mm
This is the outer diameter of the bottle neck at the thread, measured in millimeters. A 24-410 bottle has a 24mm neck opening. A 28-400 has a 28mm neck. The diameter number tells you the physical size of the opening — which governs cap fit, pour rate, and what dispensing accessories (pumps, disc tops, sprayers) can mount to the bottle.
Second number — thread style
This identifies the thread engagement profile — pitch, depth, number of turns, and where the thread starts on the neck. Two bottles with the same diameter but different thread styles are mechanically incompatible with each other's caps. The three-digit number is not a percentage or arbitrary label; it's a GPI finish code that maps to a published specification with exact tolerances.
Thread styles: -400, -410, -415, -485
The thread style number that matters most to a buyer is the difference between -400 and -410 — they look identical on the shelf and are machined on the same diameter necks, but they are not interchangeable. Here are the thread styles you'll encounter in practice:
The original GPI continuous thread finish, designed for glass containers. Thread pitch and engagement depth are optimized for rigid glass walls and standard solid caps. Approximately 7/8 of a turn of thread engagement. The dominant finish on glass bottles of any size.
Mechanically similar to -400 but with a different thread pitch and engagement profile. Designed for plastic bottles and for use with dispensing closures: pump dispensers, disc-top caps, flip-top caps, and fine-mist sprayers. The dominant finish on plastic bottles under 32 oz. Do not swap -400 caps onto -410 bottles.
A narrower-pitch CT variant used on small-diameter necks (13mm, 15mm, 18mm) where standard -400 thread geometry is too coarse for the opening. Common on essential oil bottles, nail polish, small lab vials.
A broader-pitch CT variant found on some larger plastic containers and certain European-standard bottles. Less common in the US market; verify before specifying.
A different thread geometry used on wide-mouth jars and spice containers. The 43-485 is the standard spice jar finish — used with sifter inserts, flip-top spice caps, and shaker lids. Not interchangeable with any -400 or -410 cap of the same diameter.
The #1 sourcing mistake: mixing -400 and -410
A 24-410 bottle and a 24-400 bottle have the same 24mm opening diameter. But a 24-400 cap will not fit a 24-410 bottle, and vice versa. The thread pitch is different. The cap will either stop short, cross-thread, or spin freely without seating — there is no in-between.
This happens most often when buyers source bottles and caps from different suppliers without verifying the finish code on both. The cost is the entire cap order (or the entire bottle order), plus however long it takes to re-source and reship.
Rule of thumb: if your bottle is plastic, you need -410 caps. If your bottle is glass, you need -400 caps. Verify both specs before placing any order where components come from different sources.
Glass vs. plastic: different conventions
Glass packaging almost exclusively uses -400 thread finishes. The -400 system was designed for glass, and glass molding technology produces very consistent neck dimensions that the -400 thread tolerances assume. When you see a 24-400, 28-400, or 33-400 bottle, it's glass (or a plastic bottle deliberately designed to accept glass-style caps).
Plastic bottles — blow-molded HDPE, PET, PP — are overwhelmingly -410 because the blow-molding process and the flexibility of plastic wall material work better with the -410 thread profile. Dispensing closures (pumps, sprayers, disc-tops) are designed around -410 and the slight compliance that plastic necks provide.
There are exceptions. Some plastic bottles are produced with -400 finishes specifically to accept glass-style caps — typically when the buyer wants a premium dropper, roller ball, or fine-tip applicator that is only manufactured to -400. But this is a deliberate spec decision that must be made at the bottle design stage, not something you can retrofit.
Reference: common neck finishes
Typical use cases — actual product specifications vary by manufacturer. Always verify the finish code on both the bottle and the cap.
| Finish | Diam. | Thread | Typical Applications | Material |
|---|---|---|---|---|
| 13-415 | 13mm | -415 | Nail polish, small lab vials, roller ball inserts | Glass |
| 18-400 | 18mm | -400 | 1/4 oz essential oil vials, roller balls, sample vials | Glass |
| 18-410 | 18mm | -410 | Small plastic essential oil, roller ball on plastic | Plastic |
| 20-400 | 20mm | -400 | 1–2 oz boston rounds, tinctures, dropper bottles | Glass |
| 20-410 | 20mm | -410 | 1–2 oz plastic bottles, small pump dispensers | Plastic |
| 22-400 | 22mm | -400 | Small specialty glass bottles | Glass |
| 24-400 | 24mm | -400 | 2–8 oz glass bottles, droppers, reagent bottles | Glass |
| 24-410 | 24mm | -410 | 2–8 oz plastic bottles — the most common plastic finish | Plastic |
| 28-400 | 28mm | -400 | 4–16 oz glass bottles, standard boston round (larger) | Glass |
| 28-410 | 28mm | -410 | 4–16 oz plastic bottles, spray bottles (with adapter) | Plastic |
| 33-400 | 33mm | -400 | 16–32 oz glass and HDPE bottles | Both |
| 38-400 | 38mm | -400 | 32 oz+ boston rounds, gallon jug closures | Both |
| 43-485 | 43mm | -485 | Standard spice jar — fits sifter inserts, spice caps | Both |
| 48-400 | 48mm | -400 | Wide-mouth bottles, peanut butter-style containers | Both |
| 53-400 | 53mm | -400 | Wide-mouth packer bottles, supplement containers | Both |
| 58-400 | 58mm | -400 | Wide-mouth jars, food-grade containers | Both |
| 63-400 | 63mm | -400 | Large jars, cosmetic containers | Both |
| 70-400 | 70mm | -400 | Large wide-mouth jars, quart-size food containers | Both |
| 89-400 | 89mm | -400 | Gallon jars, large wide-mouth containers | Both |
| 110-400 | 110mm | -400 | Very large wide-mouth containers, one-gallon square bottles | Both |
GPI standards: where this system came from
The finish numbering system was developed and standardized by the Glass Packaging Institute (GPI), the trade association for the North American glass container industry. GPI publishes a finish standard that defines exact dimensional tolerances for every finish code — thread outer diameter, thread inner diameter, pitch, number of turns, and the height of the neck above the bottle shoulder.
When plastic packaging took off in the 1960s and 70s, the plastics industry adopted the GPI finish numbering system rather than inventing a new one. This is why a 28-400 glass bottle and a 28-400 plastic bottle accept the same cap — the finish code means the same physical dimensions regardless of the container material. The GPI standard is referenced in ASTM specifications and has been harmonized with ISO packaging standards for most common finish sizes.
The practical implication: when a supplier lists a finish code, they are claiming compliance with published GPI tolerances. If you source a 24-410 bottle from McKernan and a 24-410 disc-top cap from Berlin Packaging, they should fit — because both are made to the same GPI specification. When they don't fit, one supplier has a quality control problem.
Quick reference
- --Buying plastic bottles under 16 oz? You almost certainly need 24-410 caps. This is the most common finish on HDPE and PET bottles in the 2–8 oz range.
- --Buying glass bottles? Default to -400. A 2 oz glass boston round is 20-400; an 8 oz glass boston round is typically 24-400 or 28-400 depending on the manufacturer.
- --Adding a pump or disc-top? Confirm your bottle is -410. Pumps and disc-tops are manufactured for -410 necks. If your bottle is -400, you need an adapter or a different bottle.
- --Buying a spice jar? The 43-485 is the industry standard. Sifter inserts, shaker lids, and snap-top spice caps are all made to this finish.
- --When in doubt, request samples before committing to full quantities. A $20 sample set of caps will tell you definitively whether they fit your bottles.
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