Vented screws are fasteners with a central vent through the center to allow the removal of gases at the bottom of a tapped hole. They may also be referred to as hollow screws.
When used in a vacuum, standard screws and fasteners will leave pockets of air trapped in various places – chiefly at the bottom of the screw thread and this “dirty air” when used in a vacuum can leak out and contaminate parts being manufactured. However, vented screw products provide a clear path for this "trapped" air to be removed by the vacuum, thereby allowing the system to reach low pressures (and stay at low pressures) more effectively.
Therefore, vented screws speed up the evacuation of air in high vacuum and ultra-high vacuum systems and promotes stable pressures and temperatures in these systems.
Socket button head vented screw available in AISI 304 or "marine-grade" 316 series stainless steel, which is extra corrosion resistant. With allen or hexagonal drive.
Vented shoulder screws are ideal for attaching panels with precision alignment whilst also allowing trapped air to escape from the bottom of the hole. Shown here in AISI 316 series stainless steel but also available in 303 series stainless steel.
Vented screws are used to remove trapped gases (at the bottom of blind threads) in HV (high vacuum) and UHV (ultra-high vacuum) systems. They can be precision cleaned and/or coated in anti-galling or hygienic films.
They are at their most effective when used with vented washers, which promote the release of gases trapped under the head of the screw.
We stock our vented screws in two grades of stainless steel - AISI 303 series stainless steel and the more expensive grade AISI 316 series stainless steel. See our stainless steel guide for more information. We also manufacture in titanium (grades 2 and 5), PEEK and other materials.
We know that corrosion resistance and cleanliness are priorities for customers choosing vented screws. We therefore can provide a range of cleaning and finishing options including ultrasonic cleaning, passivation (only for AISI 316 series stainless steel), and coatings.
Silver plating - a lubricant to reduce galling. Also antimicrobial and very hygienic. Good conductivity for heat dissipation in vacuum environments. Cheaper than gold coating.
Gold plating - to lubricate and lower chemical reactivity of the fastener (e.g. if strong cleaning agents are to be used).
Nickel plating - for added corrosion and wear resistance, improving service lifetime.
Molybdenum coating (MoS2) - a dry film lubricant to reduce galling/seizing between components.
Tungsten coating (WS2) - low friction dry lubricant that improves performance and service lifetime by reducing galling issues.
A blind tapped hole inside a vacuum system leaves residual air space at the bottom that cannot be fully evacuated in the vacuum cycle when a bolt, screw, or other fastener is threaded into the hole. The screw itself is a helix with a large surface area also containing voids of trapped air. This produces virtual leaks. Vented screws and fasteners ensure direct ventilation of these voids, allowing the trapped volumes of air within the threads and at the bottoms of the holes to be fully evacuated. This speeds pump-down and helps improve system performance.
In high vacuum and ultra high vacuum systems, similar materials can become cold-fused or seized together ("galling") due to thermal expansion and the lack of moisture created by the vacuum. Screws threaded into blind tapped holes are commonly affected in this way, and components made of stainless steel are particularly susceptible. We can reduce galling by applying various coatings and platings to lubricate components and increase fastener lifetime. This makes maintenance and replacements faster and easier. Without the hassle of galled, stuck fasteners, downtime is minimised.
Our vented and coated fasteners are inspected, cleaned, and packaged in a Class 100 cleanroom environment and therefore particulate/organic surface contamination is significantly reduced or eliminated altogether.