Equipment

Machine Screw Technical Information Guide

Grainger Editorial Staff

A machine screw is often described as small diameter bolt. Like a bolt or hex head cap screw, it features a straight, untapered shank and a blunt end, but it is usually driven with a screwdriver instead of a wrench. External machine thread runs entire length of shank.

Most commonly used to fasten metal to metal, a machine screw is designed to be inserted into a prethreaded hole or mated with a nut (in which case it may be called a stove bolt). Because application thread sizes vary, it is especially important to select the right machine screw to meet your specific requirements.

HEAD SHAPES

Binding

Has a rounded top that tapers around the edge and may have an undercut under the head.

Button

Features a domed top that protrudes above the fastening surface.

Fillister (or Cheese)

Features a relatively tall head with cylindrical sides; can be flat or rounded on top.

Flat (or Countersunk)

Has a conical head and a flat top; countersunk for a smooth, flush surface.

Hex

Head may be slotted for driving with a screwdriver or unslotted for driving with a socket or wrench.

Oval (or Raised Countersunk)

Features a countersunk head with a low-profile, rounded top that protrudes slightly above the surface.

Pan

Is a disc with a chamfered outer edge and short cylindrical sides that resembles a frying pan; has a slightly larger diameter than a round head.

Round

Has a more pronounced domed top than a button head.

Truss

Features an extra-wide, slightly rounded head with a low profile.

DRIVER STYLES

Combination

Can be driven with either a slotted or Phillips driver.

Phillips

Cross shape provides greater contact between screw and screwdriver for less slippage.

Slotted

Single slot for driving with flat-blade screwdriver.

Hex Tamper-Resistant

Special hex shape with or without center pin is ideal for use anywhere you're concerned about vandalism or theft.

One-Way Tamper-Resistant

Designed for use in permanent applications. Installs with a standard slotted screwdriver; requires special tool for removal.

Spanner Tamper-Resistant

Unique design thwarts tampering, yet allows easy installation and removal with spanner tool.

Torx® Tamper-Resistant

Star-shaped drive with six rounded points for maximum transfer of torque; provides a high level of security without sacrificing accessibility.

MATERIALS

Brass—alloy of copper and zinc that resists rust and moderate atmospheric corrosion. Not high in strength, but is durable and conducts electricity. Often used for appearance. Nonmagnetic.

Carbon Steel—contains only carbon and residual amounts of other impurities. Magnetic and malleable; can be cast or wrought.

Nylon—used extensively in electronics applications. Nonconductive, durable, and ductile material. Resists heat, corrosion, and nonacidic chemicals. Has excellent insulating properties, but dimensions can be affected by moisture absorption.

Polycarbonate—a tough, versatile thermoplastic characterized by high-impact strength, low weight, and flexibility. It provides excellent insulation in electrical applications.

Stainless Steel—contains a minimum of 12% chromium for exceptional resistance to extreme environmental conditions. Properties are highly anticorrosive. Not affected by scratching; however, not as strong as common alloy steels. Mildly magnetic.

18-8 Stainless Steel—contains approximately 18% chromium and 8% nickel. Provides excellent protection against rust and corrosion. The material of choice for prolonged outdoor use or exposure to salt spray and chemical fumes. Mildly magnetic.

Steel—the most common fastener material. Available in these types:

Alloy Steel contains enough alloying elements (other than carbon) to affect the fastener's properties; generally more responsive to heat and mechanical treatments.
Plain Steel (or Carbon Steel)—contains only carbon and residual amounts of any other impurities. It is magnetic and malleable and can be either cast or wrought.
Zinc-Plated Carbon Steel—plating provides moderate protection against rust.

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.