Brass screws are widely used fasteners composed of copper and zinc alloys, with their specific composition determining crucial performance characteristics. Understanding the copper-to-zinc ratio in brass screws is essential for selecting appropriate fasteners for applications ranging from marine environments to electrical installations. In the vast majority of brass screw alloys, copper content exceeds zinc content, typically ranging from 57% to 70% copper. This copper-dominant composition provides the corrosion resistance, ductility, and machinability that make brass screws suitable for diverse engineering and construction applications. This article examines the compositional standards of common brass screw alloys and explains how copper content influences fastener performance.

What Is Brass and How Is It Made?

Brass is a versatile metal alloy composed primarily of copper and zinc, with copper serving as the base metal. The manufacturing process involves melting copper at high temperatures (approximately 1,085°C) and then adding zinc, which has a lower melting point of 419°C. The proportion of these two metals determines the final properties of the brass alloy, including its colour, strength, machinability, and corrosion resistance.

The production of brass screws typically begins with brass rod or wire that has been manufactured to specific compositional standards. These raw materials are then formed into screws through various processes including cold heading, thread rolling, or machining. The choice of manufacturing method depends on the required precision, volume, and intended application of the fasteners.

Key characteristics of brass as a fastener material include:

• Good corrosion resistance, though this varies significantly by alloy type

• Good electrical conductivity compared to steel alternatives

• Non-magnetic properties, making it suitable for electronic applications

• Attractive golden appearance, though brass tarnishes less rapidly than pure copper but will still develop patina over time

• Superior machinability compared to many other metals

The alloying process can be precisely controlled to achieve specific mechanical properties. Manufacturers may also add small quantities of other elements such as lead (for improved machinability), tin (for enhanced corrosion resistance), or aluminium (for increased strength). It's worth noting that free-cutting brasses containing lead are generally unsuitable for potable water applications. For marine or highly corrosive environments, specialised alloys such as naval brass (CW712R/CZ112) or dezincification-resistant brass (CW602N/CZ132) are typically required.

Copper and Zinc Ratios in Brass Alloys

The answer to whether brass screws contain more copper than zinc is: yes, in the vast majority of cases. Most brass screws use alloys with more than 55% copper (commonly 57-70% Cu), so copper exceeds zinc in the composition. This copper-dominant composition is essential for maintaining the desirable properties that make brass suitable for fastener applications.

Brass alloys are broadly categorised into two main families based on their copper-to-zinc ratio. Alpha brasses contain up to 37% zinc (meaning at least 63% copper) and consist of a single-phase microstructure. These alloys offer excellent cold-working properties and are commonly used in applications requiring good formability. Alpha-beta brasses (also called duplex brasses) contain 37–45% zinc and exhibit a two-phase structure that provides enhanced hot-working characteristics and greater strength.

The copper content directly influences several critical properties:

• Corrosion resistance: Higher copper content generally improves corrosion resistance, though dezincification resistance depends on alloy design (e.g., tin or arsenic additions) and manufacturing, not copper percentage alone

• Colour: Alloys with more copper display a reddish-golden hue, whilst higher zinc content produces a more silvery-yellow appearance

• Ductility: Copper-rich brasses are more ductile and easier to form without cracking

• Strength: Moderate zinc additions (up to about 30%) increase tensile strength, but excessive zinc can make the alloy brittle

For screw applications, manufacturers carefully balance these properties by selecting alloys with appropriate copper-to-zinc ratios. The predominance of copper ensures that brass screws maintain structural integrity, resist environmental degradation, and provide reliable long-term performance in their intended applications.

Common Brass Compositions Used in Screws

Several standardised brass compositions are routinely employed in screw manufacture, each offering distinct advantages for specific applications. CZ121 (also known as CW614N or free-cutting brass) is perhaps the most widely used alloy for mass-produced brass screws. This composition typically contains 57–59% copper, 2.5–3.5% lead, and the remainder zinc. The lead addition significantly improves machinability, allowing for high-speed production of precision threaded fasteners whilst maintaining good mechanical properties.

CZ112 (CW712R, Naval Brass), containing approximately 60% copper, 39% zinc, and 1% tin, represents a premium option for screws intended for marine environments or applications requiring superior corrosion resistance. The tin addition enhances resistance to dezincification and provides excellent performance in saltwater exposure. This composition is frequently specified for boat fittings, dock hardware, and coastal construction projects.

CZ132 (CW602N, dezincification-resistant brass) contains approximately 61-63% copper, 1.7-2.8% lead, 0.02-0.06% arsenic, and the remainder zinc. This alloy is specifically designed to resist dezincification in aggressive environments and is suitable for plumbing fittings and outdoor applications where moisture exposure is expected.

Cartridge Brass (CZ106 or 70/30 brass) contains 70% copper and 30% zinc, offering a high copper content among commonly used brass screw materials. This alloy provides:

• Good corrosion resistance in diverse environments

• Superior cold-forming properties for complex screw head designs

• Excellent electrical conductivity for electronic applications

• Enhanced ductility, reducing the risk of brittle failure

CZ108 (CW508L, 63/37 brass) may also be used for certain applications. The selection of brass composition depends on factors including the operating environment, required mechanical strength, production volume, and cost considerations. Manufacturers typically provide material certification confirming the exact composition of brass screws for critical applications, referencing the appropriate BS EN standards.

Identifying Brass Screw Types by Copper Content

Determining the copper content of brass screws can be accomplished through several methods, ranging from simple visual inspection to laboratory analysis. Colour assessment provides the most accessible initial indication: screws with higher copper content (65–70%) display a distinctly reddish-gold appearance, whilst those with lower copper percentages (57–63%) exhibit a more yellow or greenish-gold hue. However, surface treatments, oxidation, and manufacturing processes can significantly alter appearance, making colour alone an unreliable definitive indicator.

Magnetic testing offers a quick verification that a screw is not brass-plated steel, as genuine brass alloys are non-magnetic regardless of copper content. However, this test has limitations—austenitic stainless steel screws are also non-magnetic, so a non-magnetic response does not conclusively confirm brass.

For applications requiring precise compositional verification, several professional methods are available:

• X-ray fluorescence (XRF) analysis: Non-destructive testing that provides accurate elemental composition within seconds

• Spectroscopic analysis: Laboratory technique offering precise quantification of all alloying elements

• Density measurement: Different copper-to-zinc ratios produce measurable density variations (pure copper: 8.96 g/cm³; pure zinc: 7.14 g/cm³)

• Manufacturer specifications: Reputable suppliers provide material certificates confirming alloy designation and composition

Practical considerations for users:

When selecting brass screws for specific applications, consult manufacturer datasheets or request material certification, particularly for critical installations. For marine, outdoor, or corrosive environments, specify dezincification-resistant brass (CW602N/CZ132) or naval brass (CW712R/CZ112) rather than relying on copper content alone. In applications where machinability during installation is important, free-cutting brass compositions offer advantages despite slightly lower copper content. Understanding these compositional differences enables informed selection of brass fasteners that will provide optimal performance and longevity in their intended service conditions.

Frequently Asked Questions