Screws

Machine and hex cap screws

• Machine screws (ASME B18.6.3 dimensions) go into a tapped hole or take a nut. Inch sizes run #0 to 1" in steel and #0 to 1/2" in 18-8. Metric sizes run M1.6 to M10.
• Hex cap screws (ASME B18.2.1 inch) come in SAE J429 Grade 5 and Grade 8, 18-8 stainless (ASTM F593 Group 1), 316 stainless, and metric Class 8.8 and 10.9.

Self-tapping, self-drilling and thread-cutting screws

• Self-tapping screws form their own thread in a pilot hole in sheet metal, plastic or wood. Types A, AB and B are stocked. All three are thread-forming.
• Self-drilling screws fasten sheet metal, steel framing, HVAC and metal roofing without a pilot hole. Choose the point number by panel thickness. Carbon steel versions follow SAE J78. 410 stainless is hardened for drilling steel. 18-8 stainless versions are for aluminum and thin or soft sheet.
• Thread-cutting screws (Types F, 1, 23 and 25) cut a machine-pitch thread in pre-drilled metal, castings and plastic. Thread-forming screws displace material instead of cutting it.

Wood and specialty screws

• Wood screws (#2 to #18) are for cabinetry, furniture and hinges. See also deck & construction and drywall screws.
• SEMS screws are screws with a captive washer.
• Security screws are tamper-resistant, with pin-in 6-lobe, pin-in hex and spanner drives. They are used on public fixtures and enclosures.
• Also stocked: thumb & wing, drive, concrete, weld and jack screws.

Screw materials and grades

Steel screws are listed as low carbon steel, or by grade (Grade 5, Grade 8) and metric property class (Class 8.8, 10.9). Alloy steel socket head cap screws are made to ASTM A574. They do not carry an SAE grade. Inch stainless is 18-8 or 316. Metric stainless is A2 or A4, often with the property class (A2-70, A4-70). Self-drilling screws also come in 410 stainless. Match the material named in the product title.

See 18-8 stainless, 316 stainless, Grade 5, Grade 8 and Class 10.9.

Screw threads and finishes

Inch machine screws are listed as coarse (UNC) or fine (UNF), for example #10-24 or #10-32. Metric threads are listed by pitch, for example M3-0.5 or M8-1.25. Tapping and wood screws list a gauge (#8, #10, #12, #14). Self-drilling screws list a gauge-TPI pair such as #12-14.

Steel finishes include zinc, zinc black, zinc yellow, black oxide and plain. Stainless is passivated, and some is black oxide; on stainless, black oxide is cosmetic. Some steel wood screws have a bright or antique brass finish. The finish is the last item in each product title.

Heads, drives and length

Heads: pan, flat (82° and 100°), flat undercut, oval, truss and modified truss, button, pancake, hex and hex washer. Drives: Phillips, slotted, square, combo (Phillips/square), 6-lobe and hex.

Length is measured from under the head to the tip. On flat countersunk heads it is the overall length. On oval heads it stops at the top of the countersink and leaves out the rounded crown.

Pack sizes and bulk boxes

Most screws come as a Package or a Bulk Box. Piece counts depend on size, for example 100 / 1,000, 200 / 2,000 or 1,000 / 10,000. Need volume pricing? See wholesale.