DIN 7504 O · Flush Finish · Window & Door Frames · Metal Cladding · ISO 15482
The DIN 7504 O countersunk head self drilling screw — also called a CSK head or flat head self drilling screw — is designed for applications where the fastener must sit flush with or below the surface of the material. The 90-degree countersunk taper pulls the head down into the material as it is driven, leaving no protrusion above the surface. Like all self drilling screws, it drills, taps and fastens in a single operation with no pilot hole required. The international equivalent standard is ISO 15482. Stocked in M3.5, M4.2 and M4.8 diameters in zinc plated and stainless steel finish.
Aluminium window frame sections to steel or aluminium substrate
Door frame assembly and installation — flush finish required
Curtain wall cladding panels and facade systems
Thin sheet metal fabrication where no head protrusion is permitted
Light gauge steel framing — partition and ceiling grid accessories
Electrical enclosures, HVAC panels and switchboard fabrication
90° countersunk head — sits flush with or below the surface when driven
Phillips drive — self-centering with high torque transfer
Precision ground drill point — drills, taps and fastens in one operation
No pilot hole required — faster installation, fewer tools on site
Zinc plated for corrosion resistance — stainless steel for outdoor and coastal
Heat treated carbon steel — hardness and torsional strength for reliable drilling
White Zinc
Stainless Steel
| Size | Length (inch) | Length (mm) | Drill Point (m/m) | Drill Capacity (m/m) |
|---|---|---|---|---|
| #6-20 M3.5 | 3/8” | 10 | #2 | 0.5 - 1.0 |
| 1/2" | 13 | #2 | 0.5 - 1.0 | |
| 5/8" | 16 | #2 | 0.5 - 1.0 | |
| 3/4" | 19 | #2 | 0.5 - 1.0 | |
| 1" | 25 | #2 | 0.5 - 1.0 | |
| #8-18 M4.2 | 1/2” | 13 | #2 | 0.5 - 1.0 |
| 5/8” | 16 | #2 | 0.5 - 1.0 | |
| 3/4" | 19 | #2 | 0.5 - 1.0 | |
| 1" | 25 | #2 | 0.5 - 1.0 | |
| 1-1/4" | 32 | #3 | 1.0 - 2.0 | |
| 1-1/2" | 38 | #3 | 1.0 - 2.0 | |
| 2" | 50 | #3 | 1.0 - 2.0 | |
| #10-16 M4.8 | 1/2” | 13 | #2 | 0.5 - 1.0 |
| 5/8” | 16 | #2 | 0.5 - 1.0 | |
| 3/4" | 19 | #2 | 0.5 - 1.0 | |
| 1" | 25 | #2 | 0.5 - 1.0 | |
| 1-1/4" | 32 | #3 | 0.5 - 1.0 | |
| 1-1/2" | 38 | #3 | 0.5 - 1.0 | |
| 2" | 50 | #3 | 1.0 - 3.0 |
The countersunk head — referred to as CSK or flat head — has a 90-degree tapered underside that is engineered to pull the head down into the material as the screw is driven. The result is a fastening point that is completely flush with, or sits below, the surface. This is not simply a cosmetic preference — in many applications it is a functional requirement. Window and door frame assemblies, curtain wall systems, sliding mechanisms and finished metal cladding panels all require flush fastening because a protruding head would interfere with seals, gaskets, finish surfaces or the movement of adjoining components.
The DIN 7504 O standard specifies the countersunk head geometry, thread form and drill point requirements for this screw type. The equivalent ISO standard is ISO 15482. Both are widely referenced in India for fenestration, facade and light gauge steel fabrication work.
90° taper — sits flush with or below the surface. No protrusion. Required for window frames, door frames, sliding systems and any finished surface where a proud head is not acceptable.
Rounded dome — sits above the surface. Standard for metal-to-metal general fastening. Not suitable where flush finish is required. Higher clamping force than CSK.
Large hex head with integrated flange — sits above the surface. Used for roofing and structural connections where a large bearing area and weather seal washer are needed.
In India, aluminium window and door frames are assembled and installed using countersunk self drilling screws on a large scale — from residential apartments to commercial complexes. The M3.5 (#6-20) and M4.2 (#8-18) sizes with Drill Point #2 are the standard choice for aluminium extrusion sections up to 1.5mm wall thickness. The Drill Point #2 cuts cleanly through aluminium without deforming the section, and the 90-degree head pulls flush into the countersunk recess in the extrusion — or self-countersinks into the aluminium surface directly.
Where window frames are fixed to a steel substrate — steel door frame surrounding, steel lintel, steel fixing bracket — the M4.2 or M4.8 with Drill Point #2 or #3 is selected based on the steel thickness. The screw must drill through the aluminium outer layer and tap into the steel behind it.
Installation note
When driving a CSK screw into aluminium, use a torque-limited driver and stop as the head reaches flush — over-driving splits the countersunk recess and weakens the joint. In thin aluminium sections, a pre-formed countersunk dimple in the extrusion gives the most consistent result.
In curtain wall and facade systems, exposed fastener heads on cladding panels are unacceptable in most architectural specifications. The countersunk self drilling screw is used to fix thin aluminium or steel cladding panels, sub-frame rails and brackets to the primary steel structure — the flush head remains hidden within the panel or behind the cladding layer.
For outdoor curtain wall use, stainless steel grade A2 or A4 countersunk self drilling screws are the correct specification — carbon steel zinc plated screws are not suitable for long-term outdoor exposure in India's coastal and high-humidity regions. Excel Trading Corporation stocks both zinc plated and stainless steel options.
| Drill Point | Steel Penetration | Screw Size | Typical Application |
|---|---|---|---|
| Point #2 | 0.5mm – 1.0mm | M3.5, M4.2 (short lengths) | Window frames, door frames, thin aluminium sections |
| Point #2 | 0.5mm – 1.0mm | M4.8 (short lengths) | Light gauge steel cladding, switchboard panels |
| Point #3 | 1.0mm – 2.0mm | M4.2 (1-1/4" and longer) | Aluminium to steel bracket / fixing point connections |
| Point #3 | 1.0mm – 3.0mm | M4.8 (2" length) | Medium gauge steel substrate, HVAC panels, enclosures |
Suitable for indoor and covered applications. Window and door frame assembly inside buildings, internal partition framing, light gauge steel fabrication in dry environments. Cost-effective for high-volume interior fenestration work.
Not recommended for: outdoor exposure, coastal locations, high-humidity environments without additional protection.
Required for outdoor curtain wall, exterior facade cladding, external window frames exposed to rain and humidity, and coastal locations across Karnataka, Tamil Nadu, Kerala and Maharashtra. Resists rust, staining and corrosion for the life of the structure.
Specify A2 stainless for standard outdoor use — A4 marine grade for highly aggressive coastal environments.
DIN 7504 O specifies a countersunk (flat) head self drilling screw with a 90-degree tapered head that sits flush with the surface when driven. It drills, taps and fastens in one operation with no pilot hole. The ISO equivalent is ISO 15482. Used for window frames, door frames, curtain wall cladding and any metal application requiring a flush surface finish.
A countersunk head sits flush with or below the surface — no protrusion above the material. This is essential for window and door frames where a raised head interferes with seals, gaskets, sliding mechanisms and finished surface aesthetics. Pan heads sit above the surface and are not suitable for these applications.
Use Drill Point #2 on M3.5 or M4.2 for aluminium sections up to 1.0mm wall thickness. Drill Point #2 cuts cleanly through aluminium without deforming the section. For fixing into a steel substrate behind the aluminium, select based on the steel thickness — Drill Point #3 on M4.2 or M4.8 for steel up to 2.0–3.0mm.
We stock DIN 7504 O countersunk self drilling screws in M3.5 (#6-20), M4.2 (#8-18) and M4.8 (#10-16). Lengths from 10mm to 50mm. Zinc plated and stainless steel. Call +91-9448239476 for bulk pricing and availability across India.
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