M4 Socket Cap Screw DIN 912 A2 Stainless Steel

The M4 socket cap screw is a cylindrical-head fastener made to the DIN 912 standard, produced in A2 grade stainless steel. Its hexagon socket allows a hex key to deliver strong clamping force in a compact footprint, which is why this size turns up constantly in enclosures, brackets, and small assemblies where a slotted or Phillips head will not fit.

This particular size and grade suits toolmakers, CNC machine builders, and workshop fitters who need a dependable M4 fastener that will not rust when it sits near coolant, condensation, or outdoor exposure. Because it is a common stock item rather than a specialty part, it is normally bought in batches to cover an entire assembly rather than one at a time.

M4 Socket Cap Screw Features

Every M4 socket cap screw here follows the DIN 912 profile: a flat-topped cylindrical head with a recessed hexagon socket, sized for a 3 mm hex key. Head diameter and height are held to the DIN tolerance, so it interchanges with existing DIN 912 screws from other suppliers.

A2 stainless steel is the standard choice for indoor and lightly exposed outdoor use. It resists surface rust from humidity, cutting fluid, and washdown far better than a plain or zinc-plated carbon steel screw, though it is softer than alloy steel and is not the right choice for very high preload joints.

• DIN 912 cylindrical head with hexagon socket drive
• A2 (18-8) stainless steel construction
• M4 thread, coarse pitch (0.7 mm)
• Requires a 3 mm hex key for installation
• Corrosion resistant in humid and washdown environments
• Consistent head dimensions for reliable countersink fit

Where It’s Used

The M4 socket cap screw turns up throughout CNC router and laser builds: securing linear rail carriages, clamping cable chain brackets, fixing sensor mounts, and holding small covers and guards in place. Its low head profile keeps it clear of moving parts and belts, which matters where clearance is tight.

It is equally common in aluminium extrusion assembly, where T-slot brackets and corner connectors are fastened with M4 screws into the profile’s slot nuts. Anyone stocking fasteners for this kind of build can browse the wider range in the CNC hardware shop.

What to Check Before Buying

Confirm the length of the M4 socket cap screw before ordering, since DIN 912 M4 screws come in a range of lengths and the wrong one will bottom out before clamping or protrude through the joint. Measure the combined thickness of the parts being joined, plus the depth of the tapped hole or nut, rather than guessing from an old screw that may be worn or corroded.

Check that a 3 mm hex key is on hand, not a similar 2.5 mm or 4 mm size, and that the clearance hole in your part actually accepts the DIN 912 head diameter — some cast or 3D-printed parts are drilled too tight. If the joint carries real load, confirm A2 stainless is strong enough; it has a lower tensile rating than grade 12.9 alloy steel.

Installation and Maintenance

Drive the M4 socket cap screw with a correctly sized 3 mm hex key rather than an oversized one that can round out the socket, and tighten to a firm hand-torque rather than maximum force, since stainless threads can gall under overtightening. Add a drop of thread locker on fasteners exposed to vibration, such as router gantries and spindle mounts.

Because A2 is an austenitic stainless steel, as the austenitic stainless steel reference explains, it can seize against another stainless part when run dry under pressure; a trace of anti-seize or light oil on the thread prevents this on screws that get removed and reinstalled often. Otherwise the screw needs no maintenance beyond a visual check for looseness after heavy vibration.

FAQ

What size hex key does the M4 socket cap screw need? A 3 mm hex key fits the DIN 912 socket on this M4 screw.

Is A2 stainless strong enough for structural joints? It suits light to medium loads; for high-preload joints, a grade 12.9 alloy steel screw is the better choice.

Will this screw rust outdoors? A2 stainless resists surface rust in humid or washdown conditions, though prolonged exposure to salt air calls for A4 grade instead.