Product Description
4-40 UNC A2 Stainless Steel Pan Phillips Head Machine Screws
These 4-40 UNC machine screws are manufactured from A2 stainless steel and feature a conventional pan head with an internal Phillips drive. The rounded pan head provides a broad bearing surface and a tidy, low-profile finish suitable for general engineering, electrical and equipment assembly.
The No.4 Unified National Coarse thread has 40 threads per inch and a nominal major diameter of 0.112 inches, approximately 2.84mm. These screws must be used with a matching 4-40 UNC nut or internally threaded component.
Available in imperial lengths from 3/16 inch to 1 inch and pack quantities ranging from 5 to 1,000.
Key Features
- 4-40 UNC imperial machine screw thread
- 40 threads per inch
- Nominal thread diameter of 0.112 inches
- A2 stainless steel construction
- Rounded pan head
- Phillips cross-recess drive
- PH1 driver size
- Suitable for matching 4-40 UNC nuts and tapped holes
- Available in packs from 5 to 1,000
Available Lengths
| Thread Size | Threads Per Inch | Imperial Length | Approximate Metric Length |
|---|---|---|---|
| 4-40 UNC | 40 TPI | 3/16" | 4.76mm |
| 4-40 UNC | 40 TPI | 1/4" | 6.35mm |
| 4-40 UNC | 40 TPI | 5/16" | 7.94mm |
| 4-40 UNC | 40 TPI | 3/8" | 9.53mm |
| 4-40 UNC | 40 TPI | 1/2" | 12.70mm |
| 4-40 UNC | 40 TPI | 5/8" | 15.88mm |
| 4-40 UNC | 40 TPI | 1" | 25.40mm |
Machine screw length is measured from beneath the pan head to the end of the threaded section.
Nominal Dimensions
| Thread Designation | 4-40 UNC |
|---|---|
| Nominal Thread Diameter | 0.112" / approximately 2.84mm |
| Thread Pitch | 40 TPI / approximately 0.635mm |
| Reference Head Diameter | Approximately 0.205–0.219" / 5.21–5.56mm |
| Reference Head Height | Approximately 0.070–0.080" / 1.78–2.03mm |
| Recommended Driver | PH1 Phillips driver |
Head dimensions are reference values for standard No.4 pan head machine screws. Confirm the dimensions of the supplied product before use where head clearance is critical.
Thread Identification
The 4-40 designation identifies a No.4 diameter screw with 40 threads per inch. UNC means Unified National Coarse, although 40 TPI is the standard coarse thread for this particular screw diameter.
These screws are not interchangeable with 4-48 UNF screws or metric M3 fasteners. Although their diameters may appear similar, the thread pitch and profile are different.
Standards Information
- ASME B1.1 covers Unified inch screw threads, including the 4-40 UNC thread form.
- ASME B18.6.3 covers inch-series machine screws and associated head styles.
- BS 1981:1991 covers unified machine screws and machine screw nuts, including recessed pan head types.
These standards are provided as dimensional and thread-form references for this product type. Confirm manufacturer certification, tolerances and material documentation before specifying the screws for safety-critical or standards-controlled applications.
A2 Stainless Steel
A2 stainless steel provides good corrosion resistance for general indoor use and many outdoor environments. It is commonly chosen for equipment, electrical assemblies and applications where an unplated, corrosion-resistant finish is preferred.
For coastal, marine, swimming-pool or chloride-rich environments, an appropriate A4 stainless fastener may provide better corrosion resistance. Suitability should be assessed for the particular environment.
Typical Applications
- Electrical enclosures and control equipment
- Electronic equipment and instrument housings
- American-manufactured machinery and equipment
- Model engineering and restoration projects
- Automotive electrical components
- Small brackets, covers and access panels
- Lighting and display equipment
- General workshop assembly
Installation Advice
Confirm that the mating nut or tapped hole has a 4-40 UNC thread. Use a correctly fitting PH1 Phillips driver and keep it aligned with the screw recess to reduce cam-out and drive damage.
Stainless steel threads can gall or seize, particularly when installed rapidly or overtightened. For assemblies that may require future maintenance, consider using a suitable anti-galling compound and tighten at a controlled speed.
Useful Links
- View all machine screws
- 10-24 UNC A2 stainless countersunk Phillips machine screws
- 6-32 UNC A2 stainless countersunk Phillips machine screws
- 10-32 UNF A2 stainless pan Phillips machine screws
- 8-36 UNF A2 stainless pan Phillips machine screws
- Metric, UNC, UNF and BSP thread data guide
- How to measure a bolt or screw
- Stainless steel thread galling prevention guide
Specifications are intended as a guide. Confirm the stainless grade, head dimensions, thread tolerances and certification before use in safety-critical or specification-controlled applications.
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