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Box of 50 black oxide socket head cap screws .31-18 x 3.5 inch

Kerr Lakeside

Kerr Lakeside .31-18 x 3.5 in. Socket Head Cap Screw Black Oxide 50 Pieces

SKU CH-CZRG-X8NHH

A pack of 50 alloy-steel socket head cap screws with a black oxide finish, .31-18 UNC coarse thread, 3.5 in. length and 180,000 psi tensile strength

  • Meets ASTM A574 and ANSI B18.3 standards for reliable structural fastening
  • Black oxide finish on alloy steel resists corrosion in demanding environments
  • Heat-treated to Rockwell C38-43 delivering 180000 psi minimum tensile strength
  • Coarse UNC thread with 1.125 in thread length ensures strong grip in tapped holes
  • 50-piece pack of .31-18 x 3.5 in socket head cap screws reduces reorder frequency

High-Strength Socket Cap Screws

This pack contains fifty alloy-steel socket head cap screws in a .31-18 by 3.5 inch size. The coarse UNC thread and partial-thread design suit general fastening jobs where high clamping force is required. The black-oxide finish adds mild corrosion resistance and a low-glare surface. They meet ASTM A574 and ANSI B18.3 standards for critical applications.

Hex Drive and Black Oxide Finish

Each screw uses a hex drive for positive engagement with standard Allen keys, reducing the risk of rounding during installation. The alloy steel body is heat-treated to a Rockwell hardness of RC 38-43 and carries a minimum tensile strength of 180000 pounds per square inch. The black-oxide coating provides a consistent appearance and meets RoHS compliance for restricted substances.

Verify Thread Fit and Length Before Use

Confirm that the .31-18 UNC coarse thread matches the tapped holes or nuts in your assembly. The overall length is 3.5 inches with a 1.125 inch thread length, so ensure the grip thickness allows full engagement of the threaded portion. The pack weighs 3.98 pounds and contains fifty pieces for batch work.

How it compares

Measured against everything we stock in Bits, Hole Saws & Accessory Kits, at today’s prices. Recalculated every night.

Price $33.99
Pricier than about 56% of the 5,493 comparable items (median $27.99).

Specifications

Product
Brand nameProspect Fastener

Questions about this item

What does the UNC .31-18 thread standard cap in practice for this socket head cap screw?

The UNC .31-18 coarse thread provides a 1.125 in. thread length on a 3.5 in. overall length, limiting full engagement to that depth in tapped holes or nuts.

What physical clearance does the socket head need to fit and mount properly?

The socket cap head requires a hex key for drive access and a countersunk or counterbored hole to seat the head flush with the surface.

How are these screws installed, and what step is often done incorrectly?

Drive each screw with a hex key into a UNC .31-18 tapped hole; the common error is over-torquing past the 180,000 psi tensile rating, which can strip threads or fracture the alloy steel shank.

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