Metal Lug Caps with Safety Button

The twist-off lug cap is the closure on most vacuum-sealed food jars. Instead of a continuous thread, it has a few angled lugs (tabs) inside that ride over and lock under matching lugs on the jar finish, so the cap goes on and off in a quarter-turn. A ring of plastisol compound inside the cap softens during processing and molds to the jar rim to form the seal.

The 'safety button' is the small raised area in the centre of the lid: under vacuum it is pulled down flat, and it pops up audibly once the seal is broken — giving consumers an instant, reliable freshness and tamper indicator.

Jam and preserve jars, honey and spreads, sauces and condiments, pickles and ferments, baby food, antipasti and gourmet products — essentially any pasteurized or hot-filled food packed under vacuum in a twist-off glass jar.

A tinplate or aluminum shell with three, four or six lugs and a ring of plastisol sealing compound, in sizes from 38 mm to 110 mm to match standard twist-off jar finishes. The button is formed into the panel. Lacquers and lithographed print give the color and branding; pasteurization-grade compound suits heat processing.

Lug caps are applied with controlled capping torque and steam or hot-fill so the plastisol seals and a vacuum forms as the jar cools and the button pulls down. Cap size and lug count must match the jar finish exactly. Too little headspace or vacuum and the button may not seat; too much and the seal weakens — both are checked on the line.

The shell is stamped and curled from lithographed tinplate or aluminum, the lugs are formed, and a precise ring of plastisol compound is lined in and cured. The button is pressed into the panel. Compound placement, lug geometry and button function are the key quality checks.