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Countersunk Head Socket

Countersunk Head Socket

Countersunk Head Socket

Not sure what size or thread you have or need?

Two ways to confirm before you order - whichever you already know about your fastener.

1If you know the fastener diameter

Open the identification guide ›

2If you have the Allen key

Match your Allen / hex key AF (across-flats) to the screw size it fits. Our reference chart covers every metric and imperial size we stock.

Open the Allen key size chart ›

Countersunk head socket screws combine the flush-fitting countersunk head of a standard countersunk screw with the high-torque internal hex (Allen key) drive of a socket screw. The result is a fastener that sits completely flush with the surface and can be driven with significantly more torque than a Phillips countersunk screw of the same size.

Also known as: Flat Head Socket Screw, CSK Socket, Allen Countersunk, Hex Socket Countersunk, FHCS.

Used in panels, brackets, machinery guards, electronics enclosures, precision equipment and any application where a flush surface is required. The 90° countersunk angle is standard metric. Install into a matching countersunk hole — use a countersink bit to create the correct taper before installation.

GRADES AND MATERIALS

Class 12.9 Black (plain finish) — Highest tensile strength, unfinished bare steel. For high-load applications where appearance and corrosion resistance are secondary. 'Black' is the industry term for uncoated plain finish.

Class 12.9 Zinc Plated — High tensile strength with a bright silver zinc finish for internal dry environments.

Class 8.8 Zinc Plated — Standard engineering grade. The most widely used countersunk socket for general machinery and structural applications.

A2-70 G304 Stainless — Marked A2, A2-70, 304 or G304. Excellent corrosion resistance for external and coastal applications. Largely non-magnetic — A small degree of magnetism from work-hardening is normal.

A4-70 G316 Marine Grade — For marine, coastal, food and chemical environments. Largely non-magnetic — Same note on work-hardening magnetism applies.

FASTENER LENGTH

For countersunk head screws, length is measured from the top of the head to the tip — because the head sits flush with the surface, the full length including the head is embedded. This is different to cap head or pan head screws where length is measured from under the head.

WHY AUSTRALIA TRUSTS BOLT & NUT

With 15+ years selling fasteners online from Brisbane, we hold over 25,000 stock lines and 200 million pieces — 98.75% of online orders placed before 1pm leave same day. Save more as you buy more — we offer up to 13 price breaks plus 3 spend-tier discounts. Read our customer reviews or get in touch if you need help picking the right socket screw.

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