Hobson UNF Countersunk Hex Socket Screw, 3/8" / 1 1/4"

The Hobson UNF countersunk hex socket screw has a UNF (Unified National Fine) thread and is plain finish. There are 13 items: 1/4" to 1/2", in lengths from 5/8" to 2". Head style: FHCS, Flat Head (Countersunk) Cap Screw.

The head is tapered so that it sits flush in a countersunk hole. UNF means Unified National Fine Thread and TPI means threads per inch. It changes with the size and length.

Where this product is used

• Fixing into countersunk holes so the head sits flush, as in jigs, fixtures and covers
• Fixture and tooling plates where the work face has to stay flat
• Sliding or rotating assemblies where nothing can stand proud of the surface
• Assemblies that will be painted, oiled or enclosed after fitting
• The 13 items cover diameters from 1/4" to 1/2" and lengths from 5/8" to 2", confirm the size against your drawing before ordering

Features

• 13 items: 1/4" to 1/2"
• UNF thread, flat head socket screw
• Plain finish
• Pack quantity shown for each item
• Uncoated plain steel: paint, oil or enclose it for protection

Key specifications

Choosing the right option

Choose the thread form first: the screw must match its nut or tapped hole in thread form, diameter and pitch.

These flat head socket screws are plain steel, with no coating beyond a light oil film, so they rust quickly in moisture. It suits dry indoor jobs, machinery, and assemblies that will be painted, oiled or enclosed. Where the job is outside or damp, move to hot dip galvanised or 316 stainless. Plain finish is normal for high-strength alloy socket screws in tooling and machine building.

UNF is the fine inch thread: the finer pitch gives more threads per inch and a finer adjustment. It only mates with UNF nuts and tapped holes of the same diameter. For load-critical, structural or lifting joints, confirm the fastener against the engineer's specification. Fasteners are not lifting rated unless marked.

Related socket screws: Hobson UNC Flat Head Socket Screw, Alloy Steel, Plain, #10-24 to 1", Hobson BSW Flat Head Socket Screw, Alloy Steel, Plain, 1/4" to 5/8" and Hobson UNC Flat Head Socket Screw, Zinc, 3/8 x 1", Box of 100.