A disc top cap is sized by the neck finish of the bottle, and its pour is set by an orifice that is chosen separately. The common series runs 18, 20, 24, 28, 33 and 38 mm, with orifices from roughly 2 mm on the smallest toner closures to about 10 mm on wide-mouth packs. A specification therefore needs three things written down, not one: the full finish code, the orifice diameter, and how the disc is locked for shipping.
What the size code tells you
A disc top (also sold as a disc top closure or press top cap) is a shell with a disc set into its rim; pressing one edge tips the disc open, pressing it flat closes it. Its size code is the same one used for any screw or press shell on that neck. A code such as 24/410 has two halves, and each answers a different question.
- The millimetre figure is the nominal neck diameter. It tells you which neck the shell goes onto. It does not describe the closure's own outside diameter, which simply follows from the tool.
- The finish designation after the separator describes the thread form and the height at which the shell comes to rest. It governs how far the shell travels down the neck and where its sealing surfaces sit against the sealing land, the flat top surface of the neck.
Necks with a shared nominal diameter and different finish designations cannot be swapped. The awkward part is that the wrong shell usually still winds on. It then seals poorly, sits high, or bottoms out with no compression left under the disc. The GPI finish definitions and similar public standards from glass packaging bodies give the dimensions behind each code, but for a real bottle we read the applied dimensions off the neck drawing instead of inferring them from the code.
Measure in the right place, too. Closure size comes from the neck finish. A tape across the threads or a reading from the shoulder will be a few millimetres out every time.
Disc top size chart
The chart converts each size into the neck family it fits, the orifice range its tooling is usually built with, and the fills that range handles. These ranges reflect closures commonly stocked for glass packaging. They are a starting point: the size and orifice for a given pack are confirmed against the neck drawing and the fill, not taken as catalogue values.
| Size | Neck finish | Usual orifice | Suitable fills | How it pours | How it locks for transport | Typical mistake |
|---|---|---|---|---|---|---|
| 18 mm | 18 mm family; fine-pitch thread with a shallow shell | Narrow, about 2 to 3 mm | Toners, essences, low-viscosity water-based fills, sample and travel packs | Thin, controlled stream that needs a tilt well beyond horizontal | Snap-shut disc, frequently with a raised tab; clear shrink band where tamper evidence is wanted | Picked for a lotion, then too slow. The hole cannot grow much before the disc loses its snap |
| 20 mm | 20 mm family; fine-pitch or deeper thread | Narrow to medium, about 2.5 to 3.5 mm | Serums, light lotions, small liquid soap packs, mouthwash samples | Small, even stream. Easy to control with thin product and slow with thick | Snap-shut disc whose spud plugs the orifice; a clip to hold the disc down is optional | Written off as cosmetics-only although small pharmacy packs use it as well |
| 24 mm | 24 mm family; fine-pitch or deeper thread | Medium, about 3 to 5 mm | Emulsions, body lotion, gels, cleansing milk, hand sanitiser | Full stream at a moderate angle. The most tolerant choice across a multi-product range | Snap-shut disc and spud, with a hinged bridge that stops it opening inside the carton | Ordered for hair oil and supplied with a cream-sized hole, so the oil runs too quickly |
| 28 mm | 28 mm family; fine-pitch or deeper thread | Medium to wide, about 4 to 6 mm | Creams, shampoo, shower gel, dish liquid, heavier conditioners | Quick pour on a short tilt; a spout moulded into the disc helps | Snap-shut disc with a deeper spud; the taller shell wall also stiffens the hinge | Expected to suit every 28 mm bottle, including ones where the finish height makes the shell bottom out |
| 33 mm | 33 mm family; wide-mouth versions intended for thick product | Wide, about 5 to 8 mm | Heavy creams, pastes, high-yield-value gels, thick condiments | Heavy but controllable, much like pouring from a jug spout | Snap-shut disc with a broad spud, commonly paired with an inner liner sealing on the land | Specified to cure a pouring fault whose real cause is an undersized neck bore |
| 38 mm (wide-mouth packs) | 38 mm family, for wide-mouth jars and tubs that take a disc in place of a lid | Wide, about 6 to 10 mm | Thick pastes, scrubs, food pastes, anything scooped or poured in a single movement | Short and heavy; closer to a wide spout than to a nozzle | Snap-shut disc with a rim lip. Once banded, the disc doubles as the tamper indicator | Swapped in for a screw lid to save money, then found to alter the label panel and carton |
Two points hold for every row. A brief that gives only the closure size is incomplete, because the orifice is drawn separately. And the neck bore matters as much as the orifice for thick product: a wide hole above a narrow bore glugs, whereas a small hole above a generous bore gives control and still leaves room for the fill nozzle.
Choosing the orifice for the fill
Size and orifice are independent. On one 24 mm neck, at one capping setting, the same shell diameter can carry a narrow hole for toner or a wide hole for hand cream. Going up a size does not widen the pour by itself, and wanting a wide pour is no reason to buy more glass.
What decides the orifice is how the product flows, not which category it is sold in. Three properties work together:
- Viscosity at the temperature of use. A cream that moves freely at 25 degrees may stand still in the neck at 15 degrees, and a product that leaves a 4 mm orifice easily in summer can hang there in a cold bathroom.
- Yield value, the stress the product needs before it moves at all.
- Surface tension, which determines whether a thin liquid drains back into the bottle after pouring or creeps across the shell rim.
Thin, water-like liquids
With toners, essences, mouthwash and alcohol-based fills, the hazard is speed, not blockage. Glass is rigid, so the user cannot squeeze to regulate the flow. Tilt angle and fill level are the only controls, which pushes more of the metering job onto the closure than a squeezable plastic bottle would. A small orifice combined with a restrictor (a small internal spout or a narrowed channel in the disc) keeps the stream controlled and makes it harder to overshoot the palm.
Lotions, emulsions and gels
These sit comfortably in the middle of the orifice range. They move under gravity at a modest angle without running away, and a mid-sized hole can be moulded to a stable dimension, so the spud closes it reliably. Brands sometimes pick a wider hole here to shorten the pour. The extra speed is then managed through fill level and the shape of the bottle shoulder, not through the closure.
Creams, pastes and other thick fills
A product with a real yield value needs a generous orifice, and the closure begins to act as a spout. The limit sits lower down, in the neck bore. Thick product squeezed through a narrow neck comes out in slugs while air is pulled back along the same path, and no disc geometry cures that. For a thick fill that is poured again and again, the honest fix is usually a wider neck. That is a decision about the glass, made before any closure is selected.
Powders and dry fills
A disc top will close a dry pack and shuts out moisture and dust better than an open shaker top. Powder flow, though, depends on humidity and the powder's angle of repose, so the hole is sized by a flow test and not by a viscosity figure. If the dry product also needs a barrier, that comes from the liner stack under the shell.
How the disc opens, closes and seals
The disc is carried on a living hinge, a bridge or a pair of ears. A thumb lifts its free edge, the disc swings or pops clear and the opening is uncovered. Pushed flat again, a spud (a small plug on the underside of the disc) enters the orifice while a bead on the disc rim clicks behind a lip on the shell. Everything happens with one hand, which is why the format persists on packs used upright on a shelf or in the shower.
Closing makes two sealing contacts at once, and they fail for unrelated reasons:
- Disc to shell, around the rim. This keeps water, dust and airborne contamination away from the orifice between uses.
- Spud to orifice. This shuts the passage so that a pack lying on its side does not weep.
Some constructions add a third: an inner gasket or liner disc compressed onto the sealing land when the shell is applied. That contact is what holds the pack sealed through transit, and it is a liner matter. The shell is only the outer half of the system, so we treat liner material, thickness and how it bears on the sealing land as part of any disc top specification that includes an inner seal.
Small differences in geometry change how each contact performs. If the disc rests slightly below the rim, the snap is not positive and light handling will open it. If it stands above the rim, it opens more easily but gathers dust at the edge and can catch on the carton during packing. The spud must be long enough to seat fully as the disc snaps home, yet not so long that repeated use splits the orifice wall. The shell wall needs enough stiffness that capper load does not distort the rim. A very thin shell can seal properly on filling day and stop staying shut a month afterwards.
Sealing and staying shut in transit
Keeping product in and keeping the disc closed during shipping are separate requirements, though quotations often merge them. Sealing is the job of the spud and, where fitted, the gasket on the land. Retention depends on the snap bead, the stiffness of the shell wall and any extra lock built into the format.
Transport locks come in several strengths:
- The plain snap, which holds until someone deliberately lifts the disc.
- A hinged bridge that must be moved aside first, or a clip folded over the disc edge.
- A shrink band or adhesive tab applied across disc and shell after capping, when tamper evidence is required, so that opening leaves a visible mark.
- Non-refillable versions in which the disc engages a one-way feature and cannot be reopened once filled. This is a different tool and a separate discussion from the standard hinged disc.
Transport complaints nearly always come back to one of three causes. A rim that lacks stiffness lets the bead release under stacking load, and the pack arrives already open. A spud that is not fully seated lets the pack weep on its side; nothing looks wrong at the filling line, and the evidence turns up later as product on the shoulder and inside the carton. And a closure with no inner seal depends on the spud alone, so a pack that spent days upside down in a warm container can pass a hand check and still have lost product.
The opposite fault matters just as much. A disc that grips too hard turns a one-handed action into a two-handed fight, and some users will give up and leave it open. Opening force comes from the snap interference and the size of the lift tab. Agree it at the sample stage, using the kind of hand that will actually operate the pack.
Fitting the shell to the neck and the capping head
Most disc tops are threaded shells, applied on the same equipment as any other screw closure. Three dimensions decide whether one runs on a given line.
- The finish. Thread pitch, thread depth and the height of the land where the shell stops. Because a shell made for one member of a finish family tends to wind onto its neighbour, the operator feels nothing wrong. The mismatch only surfaces as a failed seal or a shell sitting high.
- Shell depth against finish height. A shell deeper than the neck permits lands before the disc reaches its closed position, and load then passes through the shell instead of the seal. A shell that is too shallow leaves the snap bead short of its lip, so the disc lifts with hardly any effort. Check for both by measuring assembled height; a torque reading will not reveal them.
- Applied load. Disc top shells are generally thin-walled and moulded in a grade selected for hinge life, not rigidity. Torque that suits a solid screw cap may crack the skirt or deform the rim the disc closes against. Too little torque is no safer: the shell loosens in transit and any inner seal loses its compression.
Orientation is a further consideration. If the disc has to face a particular way relative to the label or display panel, the capping head provides that, not the closure. Head type, torque control and the rest of the equipment side are described under capping machine setup and load control.
Press-on disc tops are a different case. The glass needs a bead or groove for the shell to snap over, and that bead dimension is as critical as a thread would be. They appear mostly on sample and non-refillable packs, and they will not substitute for a threaded shell on one and the same neck, since the neck geometry differs. Reading the neck first is what stops a whole batch of closures being bought for the wrong feature.
What moving up or down a size changes
On a purchase order, one step along the series looks minor. In practice it tends to alter the whole pack.
Going up makes a wider orifice available without special tooling, which suits a thick fill and shortens the pour. The knock-on effects are larger: a wider shell requires a wider neck, which means a different glass mould and often a shorter label panel. The filled pack may stop fitting its carton, and the closure uses more material. When the bottle mould already exists, a bigger closure is seldom the inexpensive change it seems at the quoting stage.
Going down slows the pour and tightens control, a real gain for thin liquids that overshoot. The bore still has to admit the filling nozzle and whatever rinsing or cleaning device the line runs. Pouring behaviour shifts as well, because a narrow neck above a wide body glugs regardless of the closure. In cosmetic packs the neck diameter also affects how much can be tipped out, since shoulder geometry changes along with it and traps more or less product above the shoulder.
The trade-off is plain enough. A smaller closure takes less material and looks neater on a slim pack. A larger one opens more easily, tolerates thick product and pours faster, which is what someone in the shower notices. Settle the fill first, then the pour, then the size. A size picked at the outset tends to get defended instead of reviewed.
Disc top compared with flip top, pump and insert
Several closures can sit on the same bottle. The choice should follow the opening action and what the product must do once open, not bottle size or habit.
| Closure | How it works | Where it fits | Limits |
|---|---|---|---|
| Disc top | Thumb press opens a disc; product pours | Pourable product; packs that must seal flat for storage and shipping; openings that need wiping clean; a discreet look on shelf | No metering. The dose depends on the user and the fill level |
| Flip top | Lid swings on a visible hinge; a plug seals the mouth when shut | Thick fills and products applied straight from the opening; it opens further than a disc top | Stands proud when open, can be knocked open in a bag, and its larger mouth protects less against dust or oxidation between uses |
| Pump | Draws a dose up a dip tube and discharges it through a nozzle | Repeatable doses, product too thick to pour, packs used at a fixed station where a hand is free | Adds height above the shoulder, needs a dip tube cut to bottle depth, travels less freely in a bag |
| Screw cap with reducer or spout insert | Cap comes off; a separate insert restricts the pour | Lines that want more flexibility at filling | Two actions for the user, and a loose insert that can go missing |
Because the disc top shuts flusher than a flip top, keeps a smaller and cleaner opening and resists accidental opening better, it has become the default on flat-backed cosmetic and personal-care bottles. Against the cap-and-insert option, it is a single moulded assembly that keeps the reducer captive and preserves the one-handed action, with cycle life and orientation to manage in return. Relative cost between these formats is quoted per project. No option is right everywhere; what settles it is how often the pack is opened and where.
The simple rule: if the dose must repeat, specify a pump. A disc top exerts no pressure on the product, so flow is set only by gravity, tilt, fill level and orifice.
One family is excluded from this comparison. Fragrance and other crimp-closed packs carry a decorative shell over a crimped pump or sealed neck, selected for appearance and spray behaviour. Their shapes, duty and interfaces differ enough that they belong with perfume bottle caps and crimp closures. Choosing between that family and a disc top is really choosing between a product that sprays and one that pours, a call made well before closure size comes up.
Listings blur the names as well. "Disc top", "press top" and "flip top" are used loosely, and an order for a disc top can turn up as a swing-lid flip top with a different opening area and sealing contact. Here, disc top means the closed-form press top whose disc shuts level with the shell rim or just inside it; the flip top is the neighbouring format whose lid swings away on a visible hinge. Photographs do not separate them reliably. Ask for the closed height of the assembled pack and a section drawing showing disc and spud.
Cycle life and the four failure modes
A disc top is a small mechanism with a finite life. The parts that wear are the hinge or bridge carrying the disc and the snap bead holding it down. Each use flexes both, and the polymer relaxes slightly with every flex, with heat and with exposure to the product. A closure that behaves perfectly in a laboratory drawer can therefore be reported as faulty by someone who has opened the pack daily for months.
Most field reports fall into four groups:
- The disc will not stay shut. The bead has worn or the rim has relaxed, so the disc rises under its own weight or under pressure from a full pack on its side.
- The disc will not spring open. The hinge has stiffened, or product has dried in the gap between disc and rim, and the user ends up prising it with a fingernail.
- The disc bows or collapses for good. The shell was overloaded at capping, or packs were stacked while the product was still warm.
- Product weeps around the spud. The spud has deformed, a hot fill has given the orifice a set, or the gasket beneath the shell has lost compression.
No single cycle figure can be quoted, since life varies with polymer grade, wall thickness, hinge geometry, temperature of use and the product itself. It can be established for a specific pack. Take units from a production batch and cycle each one at a fixed rate until the first failure, noting which mode it was. Run the test again at a raised but realistic temperature, because heat speeds up the relaxation behind all four modes. Then set the result against the duty expected. Opening twice a week for a year and opening three times a day are very different demands, and that gap usually exceeds the gap between two candidate closures.
Two habits on the filling line lengthen service life without touching the closure. Keep the fill nozzle clean: a drip that dries across the shell rim glues the disc down, and this is the commonest reason a disc feels stuck the first time it is used. Leave enough headspace and control fill temperature as well. A hot fill cooling in a closed pack draws a slight vacuum, and a soft disc can be pulled down and held against the rim until the pack warms up or the disc is worked free.
What to send for a disc top recommendation
The chart narrows the options; four inputs finish the job. With all four we can propose a size, an orifice and a sealing arrangement together, plus the checks to run on samples before the balance of an order is committed. Unit cost, tooling, order quantity and timing all follow from that finished specification and are quoted per project.
- The fill. What it is, how it flows at the temperature of use, whether it contains oils, alcohol or solvents, and whether filling is hot or cold.
- The pour. A narrow controlled stream, a wide fast one or a spout, with a rough idea of how often the pack will be opened across its life.
- The neck. A finish code and, if available, a drawing. Finish family and finish height determine the shell; nominal diameter alone does not. If the neck is still open, the glass bottle range and its available neck finishes is the place to begin.
- The closing equipment. Torque or press application, whether orientation is needed, and the load the head can hold. A disc top that is right on the bench can be distorted by a wrong capping setting.
For fills regulated for food or cosmetic contact, the declarations required by the destination market are issued for the material actually supplied. Request them within that same enquiry; do not carry them over from an earlier pack.
Frequently asked questions about disc top caps
What does the number in a disc top size measure?
The neck. The millimetre figure is the nominal neck diameter and the designation that follows it describes the thread form and landing height of the shell. A matching diameter is not enough: with a different finish designation the shell may still thread on, yet it will seal poorly or sit at the wrong height.
Does a bigger disc top give a wider pour?
Not automatically, because the pour comes from the orifice moulded into the closure. Size only has to rise when a thick fill needs a hole larger than the shell can carry. When that happens, the neck, label panel and carton change too.
Why does my disc top weep when the pack lies on its side?
Product escapes past the spud, so check the fit between spud and orifice first, then the snap holding the disc against the rim. A deformed spud, an orifice set by hot filling or a relaxed rim can each cause weeping with no visible damage. If there is an inner gasket, look at its compression next: a shell applied at too low a load can seal early in the season and stop sealing later.
How many times can a disc top be opened and closed?
There is no universal figure. Cycle units taken from production until they fail, repeat the run at a raised but realistic temperature, and compare the outcome with how often the pack will actually be opened.
Can a disc top be used on a thick cream or paste?
Yes, as long as the neck bore is generous, since the bore is normally the true constraint. Where a thick product is poured repeatedly, choose a wider neck before choosing the closure. Where it is used at a fixed station, a pump is often the better answer.