Slotted hole

A slotted hole is a special type of opening or bore that is not round, but rather elongated and oval. It is used in many technical fields – from metal construction and mechanical engineering to roof fastening systems. Slotted holes offer greater flexibility during installation, facilitate the adjustment of components, and can compensate for temperature-related material expansion. This article explains what a slotted hole is, how it is manufactured, and its functions in construction and trade.

What is a slotted hole?

A slotted hole is an elongated, oval or slot-like opening that, unlike a classic round hole, has a longitudinal extension. It is created by:

• a combination of two semicircles and a connecting straight part,
• or by milling, punching or laser cutting into the desired shape.

Typically, the expansion is in one direction, which leads to variable positioning of screws, bolts, or connectors.

What is the purpose of a slotted hole?

Slotted holes are used to:

• 🔧 To mount components in an adjustable manner (e.g., brackets, rails, profiles),
• 🌡️ To compensate for material expansion due to temperature changes,
• 📐 To bridge tolerances during installation,
• 🪛 to allow subsequent adjustments or fine-tuning.

Especially in metal construction and in the assembly of photovoltaic systems or facade elements, elongated holes are indispensable.

Typical applications for elongated holes

1. Fastening technology

Slotted holes in mounting profiles, rails, and sheets allow screws to be moved within a certain range. This facilitates alignment and positioning – for example, with roof hooks, support rails, or brackets.

2. Mechanical and plant engineering

Slotted holes allow for precise adjustment of axles, guide rails or motor mountings, even with minimal dimensional deviations or required adjustments during operation.

3. Wood and furniture construction

Slotted holes are also used in timber construction – e.g. for hidden connecting elements or in combination with fittings to align cabinet doors precisely.

4. Expansion compensation

Materials like aluminum or steel expand when heated. Slotted holes allow movement in the longitudinal direction without deforming the component or stressing the screws.

5. Photovoltaic and facade installation

Many PV mounting systems or substructures for facade panels use elongated holes to ensure the exact alignment of rails, modules and spacing – especially on large surfaces.

Production of elongated holes

Depending on the material and application, elongated holes are created using various methods:

• 🪚 Milling: precise, variable in shape and length
• 🔩 Stamping: for high-volume serial parts
• 🔦 Laser cutting: precise and burr-free for sheet metal
• 🛠️ Drilling and filing: for individual pieces or handwork

Standards and dimensions

There is no single DIN standard exclusively for slotted holes – however, they are a component of many product standards. Common dimensions are based on screw diameters: – For M6 screws: slotted hole, e.g., 6.5 × 14 mm – For M10 screws: slotted hole, e.g., 11 × 20 mm The following applies: Hole diameter + clearance (for tolerance or adjustment range) = slotted hole size

Advantages of elongated holes

✅ Greater flexibility during assembly ✅ Compensation for manufacturing or construction tolerances ✅ Thermal expansion is possible without damage ✅ Quick and easy compensation for slopes or angles ✅ No need for re-drilling in case of minor dimensional deviations

Potential disadvantages and what to look out for

❌ Less secure connection than with classic screw holes ❌ Under high loads, the component should be secured against displacement ❌ Displacement possible due to vibration, therefore secure with a spring washer or serrated lock nut if necessary

Conclusion: Slotted holes – small opening, big effect

A slotted hole is a small but extremely versatile component. It makes assembly more flexible, simplifies adjustments, and helps prevent errors or stresses in the system. Whether in metal construction, photovoltaic installations, or mechanical engineering – the slotted hole is a proven everyday aid for greater flexibility, adjustability, and safety. More information here