A neck finish is a precise set of dimensions, and a cap fits — or leaks — based on them. Spec sheets and bottle drawings label these with letters; here is what T, E, H and I mean and why they decide cap fit and line handling.
The four key dimensions
| Symbol | Dimension | What it controls |
|---|---|---|
| T | Thread (outer) diameter | The major thread diameter — sets the cap thread size |
| E | Root diameter | Diameter at the thread root, between the threads |
| I | Bore / inner diameter | The opening — fill/pour rate and any insert or valve |
| H | Neck height | Top sealing surface down to the support ledge |
The support ledge (transfer ring)
Just below the threads is the support ledge (transfer ring) — the flange that conveyors, star-wheels and grippers hold to carry the preform and bottle through the line. Its diameter and position must match your filling equipment, not just the cap.
Thread, starts and sealing surface
Beyond T/E/I/H, a finish also fixes the thread pitch and number of thread starts (how many turns to open), and the top sealing surface where the cap liner seals. All of these must agree between bottle and cap.
Standardised finishes
This is why named finishes exist: PCO 1881, 29/25, 32/15 and the rest each bundle a complete, standardised set of these dimensions — published by bodies like ISBT (US) and CETIE (Europe) — so any matching cap and line work together. Match the neck to the closure with the neck-finish & closure guide.
How Delta specs it
Every Delta El Nile for Industry preform spec sheet gives the exact neck-finish values, and our drawings follow the standard symbols (see reading a bottle drawing). Build an RFQ with your neck finish and we will confirm fit.