
M18, Cap Head, Socket Screw (12.9).
M18, Cap Head, Bolt/ Socket Screw/ Allen Bolt, High Tensile (12.9), DIN 912, Cap Screw.
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Socket Screw is short for, 'Socket Set Screw.' The, ‘Socket Screw,’ term is used to describe a fastener that is fully threaded in lengths up to and around 1 inch (from the underside of the head. Over 1 inch in length the fastener will have a, 'shoulder,' or unthreaded area under the head. This space of unthreaded area confirms that the fastener is now a bolt (cap head, bolt in this case). A little confusing, no? Some engineers may call them screws if the person only uses the shorter length range of sizes, under an inch. Some people might simply call them Allen or, 'Allan bolts,' if they've never seen it written down in association with the Allen, Hexagonal Key. So, ‘Socket,’ refers to the hexagon shaped indentation found on the top of the fasteners’ head. Here, you can use a hexagon key (Allen Key) to tighten and loosen the fastener.
Available Materials: High Tensile (12.9 Grade) - Plain/ Self Colour and A2 Stainless Steel.
Material/ Finish |
Appearance |
Level of Corrosion Resistance |
Typical Application |
High Tensile Steel |
Self-Colour (black with no surface treatment) |
Low, without further surface treatment |
No exposure to moisture. Often Greased/ Oiled |
High Tensile Steel/ ZINC |
Shiny Metallic |
Resistant to light moisture, occasionally (not for external use) |
Low moisture environments |
A2 Stainless Steel |
Dull Shine |
External |
Intermittent weathering |
They are available in the following head types:
- Cap Head (cylinder form)
- Countersink Head (conical to fit flush)
- Button Head (rounded profile)
- Flange Button Head (including a formed washer)
- Grub/ Set (no head, just hex socket)
- Shoulder - Cap Head (plain shank wider than the end thread)
Metric Coarse and Metric Fine threads are in millimetre (mm) units and were developed to simplify the imperial systems. Europe moved to this system but the Americans choose Imperial as their default. A coarse thread has less helical coils per mm and a fine one has more. Coarse is used for heavier loads and fine is used for lighter loads prone to vibrations. Coarse threads are the, 'normal', most common versions.
Image is for illustrative purposes only.
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