SankalpA GPI or SPI finish code such as 38-400 or 28-410 describes a moulded continuous thread: the first number is the thread diameter in millimetres and the second is the thread style. A ROPP finish is drawn for a different closure, an aluminium shell with no thread until the capping head rolls one against the glass, and it carries a locking ring for the pilfer band. So a GPI or SPI finish is not the same as a ROPP finish, and a 400, 410 or 415 thread is not specified for a roll-on closure. The confusion is understandable, because at 28 mm the two measure almost the same across the threads.
Who GPI and SPI are, and what their codes cover
GPI is the Glass Packaging Institute, the North American glass container trade body whose finish standards gave the industry its numbered thread codes. SPI was the Society of the Plastics Industry, now the Plastics Industry Association, and plastic bottles adopted the same numbering. A 28-410 therefore reads the same on a glass bottle and a plastic one. The codes cover finishes for caps that arrive already threaded and are screwed on.
Roll-on pilferproof finishes are published under other systems. In India that is IS 7511 (Part 4), the Bureau of Indian Standards’ dimensions for roll-on threads pilferproof. In Europe it is the CETIE GME data sheets, such as the MCA family at 28 mm and GME 401 for the 38 mm standard ROPP glass finish. Internationally there is ISO 9056, the series of pilferproof finishes.
The two systems side by side
The notation looks alike and reads differently. In a GPI code the second number is a style reference; in a ROPP size both numbers are millimetres.
| GPI or SPI thread finish | ROPP finish | |
|---|---|---|
| Written as | 28-410, 38-400 | 28 mm standard ROSPP, MCA 3, 30 H 60; closure sized 28/15 mm |
| First number | Thread diameter, T, in mm, rounded | Nominal diameter in mm |
| Second number | Thread style: 400 about one turn, 410 about one and a half, 415 about two | Closure height in mm, where a height is given |
| Where the thread comes from | Moulded into the neck and into the cap | Moulded into the neck; formed into the cap by rollers at capping |
| Locking ring under the thread | Not part of the design | Part of the design, for the pilfer band |
| Thread pitch at 28 mm | 6 threads per inch, about 4.23 mm | 3.63 mm on the IS 7511 (Part 4) standard finish |
| Closure it takes | Pre-threaded screw cap, plastic or metal | Aluminium ROPP closure |
| Published by | GPI and SPI, North America | IS 7511 (Part 4), CETIE GME sheets, ISO 9056 |
How the second number in a GPI code is read, and the millimetre dimensions of the common codes, are set out in what 38-400 cap size means.
Does a GPI or SPI finish take a ROPP closure?
Not as specified. A roll-on closure needs two things from the glass that a GPI continuous thread is not drawn to provide: a thread profile and pitch the rollers can form aluminium into, and a locking ring the pilfer band is tucked under. The Indian roll-on standard, IS 7511 (Part 4), also requires the sealing surface to stay flat to a minimum of 0.9 mm.
The dimensions show why a caliper will not settle the question at 28 mm.
| Dimension at 28 mm | GPI 28-410 | IS 7511 (Part 4) 28 mm standard roll-on pilferproof |
|---|---|---|
| Thread diameter, T | 27.00 to 27.64 mm | 26.77 to 27.41 mm |
| Diameter at the thread root, E | 24.61 to 25.25 mm | 24.53 to 25.17 mm |
| Thread pitch | About 4.23 mm (6 per inch) | 3.63 mm |
| Locking ring diameter | None | 27.40 to 28.04 mm |
| Depth to the underside of the ring | Not applicable | 15.17 to 15.67 mm |
The diameters overlap. What separates the two is the pitch and the ring. Count the threads over a known length, or look for a raised band below the thread that is wider than the thread itself. If there is no ring, the bottle was made for a screw cap. The full steps for taking these readings are in how to measure bottle cap size, and the difference between the two closures on a line is in ROPP cap vs screw cap.
This matters for a buyer. A ROPP shell rolled onto a GPI thread has nothing to lock its band under, so it cannot show tampering, and the thread profile under it was drawn for a moulded cap rather than for aluminium to be formed into. What ROPP capping involves explains why the finish acts as the mandrel.
The finish questions buyers actually ask
Short answers to the finish questions that come up most.
| Question | Short answer |
|---|---|
| Are ROPP and GPI the same? | No. GPI codes describe screw threads for pre-threaded caps; ROPP finishes are roll-on designs with a locking ring |
| Is GPI finish 38-2000 a ROPP finish? | No. 2000 is a lug finish, which takes a twist-off lug cap. Any suffix after the code names a variant on the bottle maker’s drawing |
| Is an 18 mm ROPP finish the same as an 18-350 finish? | Do not assume so. 18-350 is written in GPI notation, where 350 names a finish style on a GPI drawing rather than a height. An 18 mm roll-on finish is drawn to a supplier’s own drawing, since IS 7511 (Part 4) starts at 22 mm. Compare the two drawings, not the numbers |
| Is a 34/400 neck finish 38 mm? | No. The first number is the diameter, so 34/400 would be 34 mm and 38/400 is 38 mm. 33 mm and 38 mm are the sizes closures are commonly stocked in, so confirm a 34 against the drawing |
| What decides a 38-400 child-resistant cap? | The mechanism is in the cap, but some child-resistant closures are made for a CRC variant of the finish, so ask which drawing the cap was made to |
Glass finishes that do take a roll-on closure, with their data sheet numbers, are listed in glass bottle neck finishes for ROPP caps, and the Indian standards behind them in neck finish standards on Indian glass bottles. Deep wine and spirits finishes are covered in BVS neck finishes.
Which finishes R Vision’s closures fit
R Vision manufactures 28/15 mm aluminium ROPP closures, supplied against MCA I, MCA II, MCA III, MCA 7.5 R, MCA 7.5 RF and PET BPF finishes. They are not made for GPI or SPI thread finishes, lug finishes or PCO plastic closure finishes. Aqua Cap is the packaged drinking water closure and Bev Cap the beverage closure, both with a TPE liner and an 8 bar rating, adhering to USFDA and EU standards. The full format is on ROPP caps. If a bottle drawing quotes a GPI code and you want an aluminium roll-on closure, the bottle has to change, not the cap; send the drawing through contact us and it can be checked.
Frequently asked questions
Is a GPI neck finish the same as a ROPP finish?
No. A GPI finish such as 28-410 is a moulded continuous thread for a cap that arrives already threaded. A ROPP finish is drawn for an aluminium shell that is threaded by rollers at capping, and it carries a locking ring for the pilfer band. At 28 mm the two overlap in diameter but differ in pitch and in the ring.
Can a ROPP cap be used on a 28-410 bottle?
It is not specified for it. A 28-410 finish has no locking ring for the pilfer band to tuck under, so the closure cannot show tampering, and its thread pitch of about 4.23 mm differs from the 3.63 mm of the Indian 28 mm roll-on pilferproof finish. Use a screw cap made for 28-410, or a bottle with a roll-on finish.
What is the difference between GPI and SPI finishes?
GPI is the Glass Packaging Institute and SPI was the Society of the Plastics Industry, now the Plastics Industry Association. The glass codes came first and plastic bottles adopted the same numbering, so a code such as 28-410 means the same thread style on glass or plastic. Always confirm against the bottle maker’s drawing.
What does the 400 mean in a 38-400 finish?
It is the thread style, not a measurement. A 400 finish has about one full turn of thread, a 410 about one and a half turns and a 415 about two. The 38 is the thread diameter in millimetres. Both numbers have to match between cap and bottle.
Is a 38-2000 finish a ROPP finish?
No. The 2000 series are lug finishes, which take a twist-off lug cap with lugs that engage short thread segments on the glass. A ROPP closure needs a roll-on pilferproof finish with a continuous thread profile and a locking ring.
How do I tell a GPI finish from a ROPP finish on a bottle?
Look below the thread. A roll-on pilferproof finish has a locking ring wider than the thread, which the pilfer band is tucked under. A GPI continuous thread finish does not. Then check the pitch: at 28 mm a GPI thread runs about 4.23 mm per turn and the Indian roll-on finish 3.63 mm.
Sources
- Glass Packaging Institute, gpi.org, the body behind the GPI finish code system.
- Plastics Industry Association, plasticsindustry.org, formerly the Society of the Plastics Industry.
- Evergreen Resources, glass neck finish dimensions, for the GPI 410 T, E and H values, converted here from inches.
- Evergreen Resources, plastic bottle neck finishes, for CRC variants such as 28-410 CRC.
- TricorBraun, long neck beverage bottle, 38-2000 lug neck finish, for 38-2000 as a lug finish.
- BIS, IS 7511 (Part 4): 1986, Roll-on Threads Pilferproof, for the 28 mm standard finish dimensions, pitch and sealing surface clause.
- CETIE, Finish data sheets (GME), for the MCA sheets and GME 401.
- ISO, ISO 9056:1990, series of pilferproof finish.
R Vision Pvt. Ltd manufactures 28/15 mm aluminium ROPP closures from Sinnar, Nashik, Maharashtra.