Metal Lug Caps with Safety Button

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

The safety button is the small raised dome in the center panel. Under vacuum it is pulled flat; once the seal is broken it pops up with an audible click, giving shoppers a simple freshness and tamper indicator.

We supply lug caps for jams and preserves, honey and nut spreads, pasta sauces and condiments, pickles and fermented vegetables, baby food and antipasti — essentially any food that is hot-filled or pasteurized and packed under vacuum in a twist-off glass jar. Retail brands, co-packers and private-label food producers use them across standard jar sizes, from small sample and gift jars up to catering formats, on both round and square twist-off jars.

Each cap is a stamped tinplate or aluminum shell with the lugs formed into the curl and a precisely placed ring of plastisol compound. The safety button is pressed into the center panel. Sizes run from 38 mm to 110 mm to match standard twist-off finishes, with lug count and depth matched to the jar. Lacquered colors — gold, white, black and silver are standard — and lithographed artwork carry the branding, and embossed panels are available on larger runs.

Lug caps are applied by steam-flush or hot-fill capping at controlled torque, so the plastisol seals and a vacuum forms as the jar cools and the button pulls down. Cap size and lug geometry must match the jar finish exactly. Headspace and vacuum are checked on the line: too little vacuum and the button will not seat, too much torque and the compound can be damaged. Send us your jar drawing and process and we’ll match the cap size and compound grade.

Shells are stamped and curled from pre-lacquered or lithographed tinplate or aluminum, the lugs are formed, and the compound is lined in and cured. Compound placement, lug geometry and button function are our key in-process checks. We match lacquer colors to your brand, print full artwork on the top panel and supply caps bulk-packed in cartons, sized and decorated to suit your jar program.