An 18 mm dropper neck is small enough that people treat all of them as one part. Three standards live at that diameter, and your range meets at least two of them when it crosses the Atlantic.
The Three Necks at 18 mm
| Finish | Thread | The cap it takes | Market |
|---|---|---|---|
| 18-400 | One full turn, short. | Dropper bulb assembly, screw cap, orifice reducer under a cap. | North America. |
| 18-415 | Two turns, taller. | Long dropper collars and tall dispensing caps. | North America, speciality. |
| DIN 18 | Its own European profile. | Tamper-evident dropper caps and child-resistant droppers. | Europe. |
The published figures for the 18 mm 410 finish, which sits between the two GPI sizes, give T 17.68 mm plus or minus 0.20, E 15.54 mm plus or minus 0.20, a bore of 8.26 mm and a height of 13.28 mm; the glass drawing reads T 17.63 mm, E 15.49 mm and a height of 13.03 mm. Your own drawing names which of the family your bottle is cut to.
Amber is a melt decision. A thin sprayed colour on flint looks the same and protects far less.
Why the Bore Matters More Than the Thread
Your dropper is a tube, a bulb and a collar, and the tube has to pass the bore with clearance. At 8.26 mm on an 18 mm neck your clearance is small, so three things get decided together: your pipette diameter, whether it is straight or bulb-ended, and whether a child-resistant mechanism shares the space.
The bore also sets your fill rate. Your viscous serum fills slowly through an 8 mm neck, so larger treatment products move to 20-410 or 24-410 even when your dropper stays the same size.
Glass Colour Belongs in the Same Decision
Most of your dropper products are light-sensitive: essential oils, tinctures, vitamin drops, serums with actives. Amber glass absorbs the band under about 450 nm and clear glass absorbs almost none of it, so the neck and the grade get specified on the same line of your enquiry. A thin sprayed colour on flint gives you the look of amber with far less of the protection, and it is a real trap in your category.
SGSBOTTLE runs amber and flint dropper glass in Shandong, on the same 14 lines that form the wider Boston round family, so a range can hold one finish across 5 ml to 100 ml (0.2 to 3.4 oz) in either colour.
What Goes on Your Enquiry
The dropper assembly you already buy or its drawing, the market it sells into, the format in ml and oz, and the glass colour. SGSBOTTLE engineers return the bottles whose finish drawing that assembly fits, with the internal height your pipette is cut to.