By Harley Kata, General Manager, The Coating House
Machine screws and cap screws both play essential roles in mechanical assemblies, but they are not the same. The differences go beyond head style or size: each is designed for specific applications, strength requirements, and installation methods.
At The Coating House, we help manufacturers, engineers, and sourcing professionals find and finish the right fasteners for their assemblies. This quick guide highlights the distinctions between machine screws and cap screws to support clearer sourcing decisions and reduce the risk of mismatched specs.
What Is a Machine Screw?
Machine screws are typically smaller-diameter threaded fasteners – often #0 through ¼” designed to be threaded into tapped holes or paired with nuts. They’re commonly used in enclosures, electronics, panels, and applications involving thin materials or low clamping force.
Common characteristics:
- External threads along the full shank
- Typically slotted or Torx drive styles
- Head styles include pan, flat, round, and oval
- Common in electronics, appliances, and control panels
- Installed into tapped holes or used with washers/nuts
What Is a Cap Screw?
Cap screws are precision-engineered fasteners designed to be installed into tapped holes and torqued to a specified value. They typically feature a flat bearing surface under the head and are manufactured to tighter tolerances than standard bolts.
Common characteristics:
- Often larger than machine screws (¼” and up)
- Socket head (Allen), hex head, and button head styles
- Higher tensile strength, often Grade 8 or alloy steel
- Used in machinery, structural assemblies, tooling, and high-load applications
- Typically governed by standards such as ASME B18.3 or ISO 4762
Machine Screws vs. Cap Screws: Key Differences
| Feature | Machine Screws | Cap Screws |
|---|---|---|
| Typical Size Range | #0 to ¼” | ¼” and larger |
| Applications | Electronics, enclosures, light-duty builds | Machinery, structural assemblies |
| Drive Styles | Phillips, slotted, Torx | Hex socket, hex head, button head |
| Tensile Strength | Low to moderate | High (Grade 8, alloy, or stainless) |
| Bearing Surface | Varies; may be formed, not machined | Flat, machined bearing surface |
| Thread Engagement | May use nut or tapped hole | Designed for precise torque in tapped hole |
| Common Standards | ANSI/ASME B18.6.3 (varies) | ASME B18.3, B18.2.1, ISO 4762 |
When to Specify Between Machine Screws and Cap Screws
Machine Screws
Use when your assembly involves thinner materials, limited torque, or components where clearance and small fasteners matter. They’re ideal for electronics housings, plastic enclosures, and hardware that doesn’t require high clamping force.
Cap Screws
Use when your assembly requires high strength, consistent torque, and structural reliability. Cap screws are preferred in precision tooling, assemblies with significant vibration, or where engineered load paths are involved.
Machine & Cap Screws by the Coating House
We supply both types of fasteners, with options for custom materials, lengths, coatings, and compliance requirements.
Our capabilities include:
- DFARS-compliant sourcing
- Pre-applied Loctite™ threadlockers and sealants
- Fastener kitting and labeling for line-side use
- Lot traceability and documentation for defense and aerospace
- Expert support in material and coating selection
Whether your drawing calls for a 6-32 Pan Head machine screw or a socket head cap screw to ISO 4762, we’ll help you source it, coated or uncoated, and ensure it’s production ready. Contact us today!