Parts of a Canning Jar – Lid, Screw Band, Rim and Threads

All 8 parts on the diagram

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Jar and lid 5

Jar A glass container with a threaded top, made for canning.
Flat lid A flat metal disc; it covers the mouth of the jar.
Screw band Screwed onto the jar, it holds the flat lid down.
Mouth The opening of the jar; regular and wide are the two sizes.
Headspace The empty space between the food and the lid.

The closed top, cut through 3

Screw threads Ridges round the mouth that the screw band turns onto.
Rim (sealing surface) The top edge of the jar; the lid seals against it.
Gasket (sealing compound) A ring of soft compound under the edge of the lid.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it. The National Center for Home Food Preservation, Recommended Jars and Lids (https://nchfp.uga.edu/how/can/general-information/recommended-jars-and-lids/), and University of Minnesota Extension, Home canning basics (https://extension.umn.edu/preserving-and-preparing/home-canning-basics), which share much of their wording and are counted as one source; Wikipedia, Mason jar (https://en.wikipedia.org/wiki/Mason_jar), Home canning (https://en.wikipedia.org/wiki/Home_canning) and Ullage (https://en.wikipedia.org/wiki/Ullage), one source. This page is not connected with or endorsed by either body. Hints and detail lines are in our own words. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; a schematic of no maker's product, nothing traced. Licence: own work

How it works

The parts of a canning jar are the glass jar and a two-piece lid: a flat lid and a screw band. The first drawing lifts them apart. The second cuts through the closed top to show how they meet.

Read the full guide

Jar and lid

The jar is glass, with a round mouth at the top. The mouth comes in two sizes, regular and wide. The flat lid is a thin metal disc that covers the mouth. The screw band is a metal ring, open in the middle, that screws on over the lid. The headspace is the empty space left between the food and the lid.

The closed top, cut through

Screw threads are ridges round the outside of the mouth; the band turns onto them. The rim is the flat top edge of the glass. Under the edge of the flat lid is the gasket, a ring of soft sealing compound. The band presses the lid down so the gasket sits on the rim.

Questions and answers

What are the parts of a canning jar lid called?

A two-piece lid has a flat lid and a screw band. The flat lid is the metal disc with a ring of sealing compound under its edge. The screw band, also called the ring, holds it on the jar.

What is the rim of a canning jar?

The flat top edge of the glass, round the mouth. It is also called the sealing surface, because the gasket under the lid presses against it.

What is headspace in a canning jar?

The empty space inside the jar, from the top of the food or liquid to the underside of the lid.

Is a canning jar the same as a Mason jar?

Mason jar is the common name for a glass canning jar with a screw thread round its mouth. It is named after John Landis Mason, who patented the design in 1858.