Custom rubber plugs & protective caps
At GUME, you receive custom rubber plugs made to measure directly from the manufacturer, including development and design support if required, from a batch size of one.
- Customised production
- Batch sizes 1 to 1 million units.
- Express production from 2 weeks
- 100% Reliability & proactivity
Rubber plugs & cover caps according to your specifications
Rubber plugs are elastic closure elements – usually designed as a moulded rubber part or moulded silicone part – for securely sealing and protecting bores, pipe ends and housing openings in industrial applications. Rubber plugs reduce vibrations and provide reliable protection against dirt and moisture. They can also be designed as a rubber-to-metal bonded part, rubber-to-plastic bonded part, rubber-to-fabric bonded part or moulded TPE part.
As a rubber plug manufacturer with 35 years of experience, we at GUME produce tailor-made plugs to your specifications for industrial applications.
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Structure of rubber stoppers / covers
At GUME, silicone plugs and rubber plugs are produced specifically and individually to meet customer requirements. The geometry of the plug can be influenced by several parameters to find the exact solution for your challenge:
Height (h1)
The more friction and sealing effect that is to be achieved, the higher the plug body is designed by the rubber stopper manufacturer. Long rubber stoppers are harder to fit, which is why the maximum length is often limited.
Height of the stopper head (h2)
A higher head is often used for easier assembly and disassembly, as it offers a larger contact surface for applying tensile forces, and the silicone or rubber plug becomes easier to handle. If the rubber plug is used for aesthetic reasons, for example to conceal a screw underneath, the plug head is colour-matched to the surrounding material and chosen to be rather flat so as to be less noticeable.
Geometry of the stopper body
Depending on whether a round, oval or rectangular opening is to be sealed, the basic geometry of the stopper body is adapted accordingly. The rubber stopper is designed in such a way that it closes the opening precisely or overlaps slightly by adjusting the diameter or length and width. A tight fit ensures a tight fit and high tightness, while a looser fit with more play is used for easier installation with a lower sealing effect and lower mechanical requirements.
Outer contour of the plug body
To anchor the rubber plug in the opening, the surface is adapted with ribs, fins, and threads. Fin plugs or plugs with ribs can fold inwards, providing greater grip and sealing effect. Threaded plugs are only used when pronounced threads are to be sealed. Due to their elastic properties, conical or ribbed plugs, which can be directly fitted onto the threads, can also be used for light threads.
Essays
For easier installation or removal, the rubber stopper manufacturer inserts a handle, a slot, a cross slot or a hexagonal opening in the stopper head.
Rubber materials for your Rubber plugs & caps
Depending on the operating environment and the requirements of your plug or cover, we work with you to select the right material for processing from a wide range of suitable elastomer materials.
Contact us for free material consultation for your application!
Sectors / Applications for Rubber plugs & caps
Plugs and cover caps are used in a variety of industries, including mechanical and plant engineering, medical technology, aerospace, and construction and infrastructure.
They reliably cover and protect openings, connections and sensitive areas and, where required, seal them securely.
Plugs & Covers in Mechanical Engineering
In mechanical and plant engineering, rubber and silicone plugs are used for process-reliable sealing and to protect sensitive interfaces. Typical applications include closing hydraulic and pneumatic connections during transport and assembly, sealing threaded bores in gearbox housings and temporarily closing cooling and lubrication channels during pressure tests. Silicone plugs are used at higher temperatures, for example in painting or drying processes, as they remain thermally stable and dimensionally stable.
Plugs & Covers in the Medical Technology
Rubber and silicone plugs are used to reliably seal housings, cartridges, fluid channels and sample containers. They close sterile openings on diagnostic devices, pump systems or laboratory instruments and prevent the ingress of germs as well as the leakage of sensitive media. Thanks to their biocompatibility and sterilisability, silicone cover caps (VMQ/FVMQ) are suitable for autoclave, EO or gamma sterilisation processes. Validated compounds, low extractables, documented traceability and a reproducible sealing function are crucial.
Plugs & Covers in the Aerospace industry
Rubber and silicone plugs are used in high-stress technical systems, for example, to protect hydraulic connections on actuators, to temporarily seal bores in structural components, or to seal cable glands in avionics housings. They secure fuel lines, sensor ports, and maintenance openings during assembly, transportation, and service. High-quality rubbers such as fluorosilicone or FKMCompounds can also withstand kerosene, hydraulic oils, and extreme temperature fluctuations. Important in the aerospace industry are rubber caps and plugs with low outgassing, stable mechanical properties under vibration, and long component availability.
We manufacture every plug & cover geometry.
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- 100% in-house expertise
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Insights into our customers'
cover cap and plug projects.
Secure protection for drill holes and threads permanently improved
The challenge
A customer from the plant engineering industry needed plugs/caps to protect threads, holes and connection points during assembly, transport and storage. However, the standard parts previously used did not fit securely enough, came loose due to vibrations and did not provide a permanently reliable fit in the event of temperature fluctuations. This repeatedly resulted in soiling and additional work during final assembly.
Implementation
We analysed the installation situation, the tolerances of the protection points and the mechanical loads together with the customer. The geometry of the stopper was adapted on this basis, including an optimised lamella and clamping contour for a tighter fit. In addition, we selected an elastomer material that is sufficiently flexible for assembly and at the same time offers the necessary restoring force for a secure seal and cover.
Solution
Thanks to the customised geometry and the coordinated material, the plugs and cover caps could be reliably held in position. Threads and openings remained clean and protected during the process steps, assembly problems were reduced and the handling effort was significantly reduced. This provided the customer with a customised protection solution for their application.
Do you have questions about plugs and covers?
We have answers!
How quickly can custom rubber stoppers be delivered by GUME?
While our standard deliveries typically take 8 weeks, you benefit twice over with our express option: you'll have your samples in hand in up to 2 weeks, and you can start series production in just 4 weeks. We see ourselves not just as rubber plug manufacturers, but also as development and system partners for rubber solutions. This also includes doing everything possible for our partners when it matters.
For what purpose is which rubber stopper geometry suitable?
The choice of geometry depends on the installation situation and functional requirements. A cap protects bolts or threads from dirt and damage. Flat plugs seal flat boreholes flush. Handle plugs allow for frequent manual removal. Cone plugs seal conical openings flexibly. Lamellar plugs compensate for tolerances and sit securely in thin-walled tubes. Oval plugs and rectangular plugs seal profile pipes positively. Screw plugs are screwed into threads and offer high holding force. Classic closing plugs serve as a universal solution for simple, static seals without disassembly requirements. Shaft caps for rifles and tools are available in various strengths and Shore hardnesses to adjust handling individually and dampen vibrations.
How is the correct Shore hardness for a rubber stopper determined?
The correct Shore hardness is determined by the sealing requirement, insertion force, tolerance compensation, and ease of disassembly. Softer compounds (e.g., 40–50 Shore A) conform better and seal reliably with larger tolerances, but may have lower holding forces. Harder rubber compounds (<60 Shore A) increase dimensional stability and pull-out force. The interaction between geometry, material, and the actual installation situation is crucial, ideally validated by testing. We are happy to assist you in selecting the appropriate material and testing various options for your rubber plug.
Can rubber stoppers be combined with metal, plastic or fabric?
Yes, rubber stoppers can be specifically combined with metal, plastic or fabric. Metal inserts provide additional stability, plastic components enable complex geometries with greater rigidity and low weight, while fabric reinforcements increase the resistance to pressure and tearing. In this way, rubber stopper composite solutions are created that optimally combine mechanical strength, sealing effect and ease of installation - at GUME always precisely customised to your application.
How is the sealing effect of a rubber plug ensured?
The sealing effect of a rubber or silicone stopper is based on elastic compression and the resulting surface pressure between the stopper's outer contour and the bore wall. A defined interference fit creates radial compression during insertion, which is higher than the applied pressure. Geometric elements such as lamellae, sealing beads, or cone angles control the contact pressure and tolerance compensation. Material parameters like Shore hardness, Young's modulus, and compression set influence relaxation and long-term sealing. Additionally, surface roughness, lubrication condition, and temperature and media exposure are significant for permanent sealing.
Are rubber stoppers suitable for food or medical applications?
Yes, rubber stoppers are suitable for food or medical applications, provided that suitable compounds are used. Conformities such as EU 1935/2004, FDA or specific medical standards are decisive, which are ensured by the use of tested raw materials and documented traceability.
