Understand the diameter of the neck of the glass bottle

Jun. 12, 2025

To determine the diameter of the bottle cap, please measure from one side of the inner wall to the other side. Measure the diameter of the outermost thread to calculate the bottleneck. The resulting millimeter measurement is the "T" dimension.

Number of Turns of the Bottle Cap Thread

Quick Reference Table

GPI Finish Code	Image	Key Parameters & Description	Thread Type	Turns	Thread Pitch (TPI)	Sealing Location	Common Use & Features
24-410		"T" Dimension: 24mm inner bore diameter	Continuous Thread	1.5 turns	10 TPI	Usually seals on top edge	Common food jar finish (e.g., jam, salsa)
		Standard continuous thread finish
XX-400		Continuous thread finish	Continuous Thread	1 turn	8 TPI	Usually seals on top edge	Older style, less common than 410, often used for chemical bottles
		Older style, coarser threads
XX-415		Continuous thread finish	Continuous Thread	2 turns	8 TPI	Usually seals on top edge	Requires taller cap, used for wider mouth products like some nut butter jars
		Taller "H" dimension (overall glass finish height)
XX-425		Continuous thread finish	Continuous Thread	2 turns	8 TPI	Usually seals on top edge	Similar applications as 415
		Narrower/thinner thread profile
XX-430		Buttress thread finish (asymmetric profile: steep and shallow sides)	Buttress Thread	2 turns	6 TPI	Seals on top bead	Used in pressure applications (e.g., carbonated beverages like beer, soda), very secure seal
		Thick, wide threads
		Top bead present
XX-2000		Lug finish (3,4, or 6 lugs instead of continuous thread)	Lug Finish	Less than 1 turn (¼ to ½ turn)	N/A	Cap lugs engage under glass lugs	Twist-off caps for beverage bottles (e.g., beer, soda, ready-to-drink teas)
		Cap has matching lugs; placed and turned less than a full rotation to lock

How to Actually Identify a Bottle Finish

Measure the "T" Dimension: Use digital calipers to get the inner bore diameter (ID) in mm.

Visually Identify Key Features:

• Continuous thread? Lug? (Non-continuous).
• Approximate number of thread turns (1, 1.5, 2)? (For continuous thread).
• Is there a prominent top bead? (Indicates 430 or similar).
• Are the threads thick/buttress shaped? (Indicates 430).
• Measure Thread Pitch (Optional but helpful): Use a thread pitch gauge (Imperial - TPI) to measure the number of threads per inch on a continuous thread finish.
• Result: You get the full finish designation (e.g., 24-410, 28-400, 38-430, 43-2000).

The "bottleneck size" for capping is defined by the GPI Finish Designation (e.g., 24-410).

T Dimension = Inner Bore Diameter (mm). Measure with calipers.

Finish Code (e.g., 410) = Standardized code defining thread type, turns, pitch, and sealing surface. Determined by visual inspection and comparison to standards.

The fraction-like notation (e.g., 24/410) is simply shorthand for the full GPI finish designation 24-410, combining the T-dimension and the finish code. The denominator (410) is not a measurement you take directly; it's a code representing the thread design specifications.