M2.5 A4 Stainless Countersunk Socket Screws DIN 7991

Product Description

M2.5 × 0.45mm A4 stainless-steel countersunk socket set screws, fully threaded and available in lengths from 4mm to 20mm.

These corrosion-resistant metric screws feature a flat countersunk head and an internal 1.5mm hexagon drive. When installed into a correctly formed countersink, the head can sit flush with or below the surrounding surface, making these screws suitable for compact machinery, instrumentation, marine equipment, electronics and precision engineering assemblies.

• Thread size: M2.5
• Thread pitch: 0.45mm metric coarse
• Threading: Fully threaded – see verification note below
• Available lengths: 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 16mm and 20mm
• Head style: Flat countersunk socket head
• Nominal head diameter: Approximately 5mm
• Nominal head height: Approximately 1.5mm
• Drive type: Internal hexagon / Allen key
• Allen key size: 1.5mm
• Material: A4 stainless steel
• Comparable stainless type: Commonly associated with 316 stainless steel
• Finish: Natural stainless-steel finish
• Traditional standard: DIN 7991
• Current international standard: ISO 10642
• British adoption: BS EN ISO 10642
• Pack sizes available: 5, 10, 20, 50, 100, 250, 500 and 1000

These M2.5 countersunk socket screws are suitable for marine fittings, instrumentation, electronics, model engineering, small machinery, brackets, covers, panels and precision mechanical assemblies.

The standard M2.5 × 0.45mm metric coarse thread must be used with a corresponding M2.5 nut, threaded insert or tapped hole. It is not interchangeable with M2, M3 or non-metric thread forms.

The flat countersunk head is intended to fit into a matching countersunk recess so that the top of the screw can sit flush with the surrounding component. The countersink angle and depth should be checked before installation to ensure that the head bears correctly against the mating surface.

Countersunk socket screws have reduced loadability compared with conventional cylindrical socket cap screws because material is removed from the head to form the countersunk profile and internal hexagon recess. They should not automatically be substituted for standard socket cap screws in highly loaded joints.

A4 stainless steel contains molybdenum and generally provides improved resistance to moisture, salt spray and many corrosive environments compared with A2 stainless steel. It is widely selected for marine, coastal, exterior, food-processing and chemical-processing applications.

The term “marine grade” indicates improved corrosion resistance but does not mean that the fastener is immune to corrosion in every environment. Temperature, chemicals, crevices, surface contamination and contact with dissimilar metals can all affect service life.

Stainless-steel threaded fasteners can suffer from galling or cold welding, particularly when installed quickly, tightened dry or used with a stainless-steel mating thread. A suitable anti-seize compound and controlled installation speed may help reduce this risk.

Use a correctly fitting 1.5mm Allen key or hex socket bit and ensure that it is inserted fully into the recess before applying torque. Small internal hexagon drives can be damaged if an undersized, worn or incorrectly seated tool is used.

Unlike most raised-head screws, countersunk screw length is normally measured over the complete screw, including the countersunk head. Check the required overall length and countersink depth before ordering.

Please note: DIN 7991 is the traditional product designation. ISO 10642 is the current international standard for hexagon socket countersunk head screws, with BS EN ISO 10642 being the corresponding British adoption. Specifications are intended as a guide only and may vary within permitted manufacturing tolerances. Check the fastener where dimensions, load capacity, fit or corrosion performance are critical.

Please Note: Specifications given are intended as a guide only. If critical to your project please check with us first.