Rubber Stoppers: Materials, Types & Custom Sizing for Lab & Industry

Rubber stoppers are among the most universal sealing components — from a chemistry lab flask to an industrial fitting. Yet “just send a stopper” often fails, because the material, hardness, and hole pattern decide whether it seals, survives the media, and meets compliance. This guide covers stopper materials, types, and how to get custom sizes molded to your sample or drawing.

What Rubber Stoppers Are Used For

• Lab & pharmaceutical – sealing flasks, tubes, and connectors; holding probes and stirrers.
• Industrial – plugging ports, isolating vibration, and cushioning in equipment and enclosures.
• Consumer & appliance – feet, caps, and dampers where a soft, grippy seal is needed.

Choosing the Right Material

For chemical- and temperature-specific guidance, see the material specification library.

Solid vs. Holed Stoppers

Stoppers come in four common configurations:

• Solid – a complete plug for sealing an opening.
• 1-hole – passes a single tube, probe, or wire.
• 2-hole – passes two lines (e.g., gas in / out).
• Custom-drilled – off-angle or multiple holes to a drawing.

The hole must be a controlled interference fit on the inserted item; too loose leaks, too tight splits the stopper. For standard sizes, dimensions often follow the same nominal logic as the AS568 O-ring size chart — match ID and cross-section to the port.

Hardness and Fit

Most stoppers are molded between 40 and 70 Shore A. Softer stoppers grip better and seal irregular openings; harder ones hold a precise hole and resist compression. The Shore A hardness guide explains how to trade conformance against extrusion and wear.

Food & Medical Compliance

For food, beverage, and pharmaceutical contact, specify silicone or selected EPDM grades to FDA and USP Class VI. Anlintech supplies certified compounds with lot traceability and material documentation on request.

Custom Rubber Stoppers

Anlintech compression- and injection-molds stoppers to custom diameters, tapers, hole patterns, and durometers in silicone, EPDM, NBR, and other compounds. Send a sample or drawing — including the port size, media, temperature, and whether holes are required — and we will produce a first article for verification before full tooling. Standard and custom O-ring cross-sections are also available from the AS568 size chart for integrated sealing designs.

Related Resources

• AS568 O-Ring Size Chart — standard sizing for integrated O-ring seals.
• Material Specification Library — temperature, hardness, and chemical-resistance data.
• Low-Volume & MOQ Guide — how small-batch custom rubber parts are quoted.