A cap that screws on by hand tells you almost nothing. A cap that holds a vacuum through pasteurisation, survives a drop test and comes off at the torque your consumer can manage is a different question, and it is settled on paper before a container is committed. Nine checks cover it, in the order they cost money: the finish, the seal, and your line.
The 9 Checks
| Step | Check | Settled by |
|---|---|---|
| 1 | Finish designation on the bottle and the closure match. | The product page and your closure order. |
| 2 | The finish drawing's T, E, I, S and H sit inside your cap's tolerance. | The drawing on your quotation, read by your closure supplier. |
| 3 | Finish family suits the closure type: CT, lug, crown, ROPP, crimp or cork. | The neck finish library and your closure type. |
| 4 | Sealing surface is flat, undamaged and wide enough for the liner. | 100 percent finish inspection at the base, plus ISO 9885 for wide mouths. |
| 5 | Liner material suits the product and the fill temperature. | Your closure supplier, from the fill you name. |
| 6 | Application and removal torque are in range for the finish size. | Your closure supplier's torque table, checked on the sample. |
| 7 | Tamper band or lug count has the bead and the geometry it needs. | The finish drawing, and a cap sample on a real bottle. |
| 8 | The capping head runs the finish without a change part. | A sample run on your own line. |
| 9 | Decoration and labelling leave the sealing surface alone. | The decorated sample you sign off. |
Checks 1 to 3: The Finish Itself
The designation comes first because it is the cheapest thing to get right. A 28-400 cap and a 28-400 bottle are made to the same published figures, and so are a 63 TO cap and the 63 mm lug jar under your 380 ml (13 oz) preserve line. Two suppliers quoting you the same designation are quoting parts intended to mate.
Then the drawing, because a designation is a family and a drawing is a bottle. Your closure supplier reads the T, E, I, S and H from the finish drawing on your quotation and confirms the cap lands inside the tolerance band. Glass drawings and plastic charts differ by a few hundredths of a millimetre in the same nominal size, so the drawing settles it and a chart never does.
Then the family, because a diameter is not a fit. On a 750 ml (25 oz) spirits bottle, a ROPP finish and a CT finish at 28 mm take different closures and different capping heads: the ROPP thread is rolled onto the glass by your line, and the CT thread is already there. A crimp perfume neck, a bar-top bore and a crown lip each rule out everything else. The neck finish library sets the families out with the standards behind them.
Your seal happens on a ring of glass a few millimetres wide, and every base inspects it before packing.
Checks 4 to 6: The Seal
The seal happens on a ring of glass a few millimetres wide. A chip, a dip or a line across that sealing surface is a leak, so every bottle gets a finish and sealing-surface inspection before packing at both SGSBOTTLE sites. Shandong checks by machine with an inspector behind it, and Xuzhou checks 100 percent of pieces by hand. On a wide-mouth jar, ISO 9885 governs how flat that ring has to be, because a vacuum lug cap presses a gasket against it.
The liner does the other half. On a 500 ml (17 oz) bottle as much as on a 30 ml (1 oz) one, foam, pulp-and-foil, plastisol, induction-seal foil and a plug seal all behave differently under heat, vacuum and pressure, and your closure supplier picks from the product and the fill temperature. Name the fill and the temperature on your enquiry: a hot fill at 85 °C, a pasteurised beer, a cold-filled 250 ml (8 oz) juice and a dry spice each get a different answer.
Torque closes the loop. A cap applied too loosely vents, and a cap applied too tightly crushes the liner or strips the thread. Your closure supplier publishes an application and removal torque range for the finish size, and the number to check is the removal torque on a bottle that has been through your process, because that is what your consumer meets.
A pump, a dropper and a sprayer each fix a finish, so the closure you already buy decides your bottle.
Checks 7 to 9: Your Line
A tamper band needs a bead to break over, and a lug cap needs the lug count the finish was cut for. Both live on the drawing, and both are worth checking against a real cap on a real bottle rather than against a description.
The capping head is the check that catches what paper misses. Chuck height, pick-up, the star wheel and the bottle's own verticality all bear on whether a finish that measures correctly also runs at speed. A sample run on your own line is the only test for it, which is what the sample stage exists for: free samples on any of the 10,000+ stock SKUs SGSBOTTLE holds in Shandong, and 5 to 10 decorated samples off the sample mould on a custom project.
Decoration comes last and matters more than it looks. Frosting, spray coating, screen printing and labelling all belong on the body, and none of them belongs on the sealing surface. A decorated sample from the Shandong deep-processing plant, opened in 2020, confirms that the coating stops where it should and that your label adhesive holds on the surface you chose.
What to Send for a Cap Match
Four things, and a cap match comes back with a drawing attached: a sample of the cap you run today or its drawing, the finish designation if you know it, the fill and its temperature, and the capping head or the line the bottle has to run on. SGSBOTTLE engineers return the stock designs whose finish drawing that cap fits, so your capping line stays exactly as it is. Where nothing in stock fits, a finish goes into the mould at the sample-mould stage and the decorated samples that come off it are the ones your line tests.