Screws
Phillips Pan Screw with Inserted Plain & Spring Washer
The Phillips Pan Screw with Inserted Plain & Spring Washer is a cold-forged SEMS fastener combining a pan head, cross-recess drive, and pre-assembled captive washers in a single component. Accurate Fastners supplies this assembly-efficient screw in SS 304 and SS 316 for M4 to M6 metric sizes.
- Standard
- —
- Grades
- 304 / 316
- Size
- M4 – M6
- Length
- On enquiry
Verification note: No dedicated image was supplied; this page shares the combination washer screw image.
Overview
What is the Phillips Pan Screw with Inserted Plain & Spring Washer?
A SEMS screw — an acronym derived from 'screw and washer assembly' — is a fastener manufactured with one or more washers permanently captured beneath the head before the thread is rolled. In this variant, both a plain washer and a spring washer are retained together, meaning the component arrives at the assembly line as a single piece rather than three separate parts. This reduces the risk of missing washers and simplifies parts management across production runs.
The head form is a pan head, which presents a low-profile, slightly domed top surface with a large bearing diameter relative to its height. Drive engagement is provided by a Phillips cross recess, one of the most widely used positive-drive profiles in automated and hand-assembly operations. The captive plain washer distributes the clamping load over a broader contact area on the mating surface, while the spring washer — typically a split-ring type — introduces a degree of elastic resistance that may help resist vibrational loosening under service conditions.
Cold forging is the manufacturing process used to form these screws. In cold forging, wire stock is shaped at ambient temperature under high pressure, which refines the grain structure of the stainless steel and generally produces tighter dimensional consistency compared with machined equivalents. The thread is metric, conforming to standard pitch conventions, so the screw is compatible with the wide range of metric-threaded inserts, nuts, and tapped holes used across industrial sub-assemblies. The size range of M4 to M6 covers light-to-medium duty panel and component fixing requirements.
In Depth
Product description
Construction & Geometry
The screw body is cold forged from stainless steel rod, producing a one-piece shank and head with consistent mechanical properties throughout. The pan head features a flat underside that bears squarely onto the plain washer. Both washers are captured below the head during manufacture and cannot be separated from the screw body under normal handling, making the assembly a discrete stock-keeping unit with a defined sub-assembly count of three functional elements.
Metric threading runs along the shank in standard pitch for the respective diameter. The Phillips recess is formed to accept a standard PH-series driver bit, ensuring compatibility with common powered and manual screwdrivers. The spring washer sits between the plain washer and the bearing face of the head, so when the fastener is driven home, the spring washer is compressed before the plain washer makes full contact with the joint surface, preserving the load-spreading function of the plain washer throughout.
Functional Behaviour in an Assembly
During installation, the plain washer spreads the axial clamping force across a larger footprint on the substrate, which may reduce surface indentation on softer parent materials such as aluminium extrusions or thermoplastic housings. The spring washer, once compressed, exerts a continuous reactive force against the bearing surfaces. This may help maintain residual clamp load if minor settlement or relaxation occurs in the joint over time, particularly in assemblies exposed to vibration or thermal cycling.
Because the washers are captive, they rotate with the screw head during driving and do not require a technician to hold or position them independently. This characteristic is particularly useful in automated screwdriving stations where loose components could interrupt the feed mechanism. The pre-assembled format also reduces the risk of incorrect washer sequencing — a concern in quality-controlled production environments — since the correct combination is built into every fastener before it leaves the manufacturer.
How It Differs from Similar Fasteners
Compared with a plain pan-head Phillips screw used with loose washers, the SEMS format eliminates separate washer procurement, storage, and placement steps. Against a screw supplied with only a spring washer, the dual-washer combination adds the load-distribution benefit of the plain washer underneath, which can be important when bearing on coated or sensitive surfaces. The captured arrangement also means torque values and installation procedures can be standardised more reliably across a production batch.
Relative to a hexagon-head bolt of equivalent diameter, the Phillips pan SEMS screw offers a lower installed profile and requires a rotary driver rather than a spanner, making it more suited to recessed or space-constrained locations. It is not intended as a structural tension fastener; its primary role is panel attachment, cover fixing, and component mounting where a neat, self-contained fastener is preferred over separate bolt-and-washer assemblies.
Material & Grade
Material and grade information
- SS 304
- SS 316
These screws are available in SS 304, an austenitic stainless steel containing approximately 18% chromium and 8% nickel. SS 304 offers good general corrosion resistance in mildly corrosive indoor environments and is commonly specified for food processing equipment, general machinery enclosures, and LED lighting fixtures where exposure to aggressive chemicals is limited. Its relatively good formability makes it well suited to the cold-forging process used to manufacture these screws.
SS 316 contains an addition of approximately 2–3% molybdenum, which typically improves resistance to chloride-containing environments compared with SS 304. It is commonly selected for applications in pharmaceutical machinery, marine-adjacent installations, or where cleaning agents containing chlorides may be present. For any application where the grade selection is critical to service performance, it is advisable to confirm the appropriate choice with the Accurate Fastners sales team based on the specific operating environment.
Grades shown are those documented for this product in the Accurate Fastners brochure. General material notes are guidance only; confirm grade selection for your environment.
Technical Data
Technical specifications
| Product type | Screw – Phillips Pan Screw with Inserted Plain & Spring Washer |
|---|---|
| Material | Stainless steel |
| Material grade | SS 304, SS 316 |
| Nominal diameter / size | M4 – M6 |
| Length | To be confirmed on enquiry |
| Thread type | Metric |
| Head / form | Pan head with captive plain and spring washer |
| Drive / tightening | Phillips cross recess |
| Manufacturing process | Cold forged |
Sizes
Available sizes
Documented size range
M4 – M6
Documented length range
On enquiry
Individual sizes within the documented range, thread pitches and lengths are confirmed at quotation stage.
Applications
Industrial applications
RO Water Purifier Assemblies
Pan SEMS screws may be used to secure housing panels, filter brackets, and cover plates on RO purifier units, where the captive washer combination helps protect coated or plastic sub-panels from surface marking during tightening.
Solar Energy Mounting Structures
In solar panel sub-frames and junction box covers, the pre-assembled washer format supports consistent clamping across batches, and SS 316 may be selected where prolonged outdoor exposure or coastal proximity is a consideration.
LED Lighting Fixtures
Lightweight LED driver housings and heat-sink assemblies commonly require M4 to M6 fasteners with a low head profile. The Phillips pan SEMS screw suits these applications while keeping the parts count at each assembly station to a minimum.
Pharmaceutical Machinery Panels
SS 316 SEMS screws may be appropriate for access panels and guards on pharmaceutical processing equipment, where smooth, easy-to-clean surfaces and resistance to frequent wash-down are desirable characteristics.
Food & Beverage Equipment
Enclosure covers and inspection panels on food-grade machinery benefit from the dual-washer arrangement, which distributes load evenly and reduces the risk of surface damage to coated or polished substrates during routine maintenance retightening.
Features & Selection
Features and selection considerations
Design features
Captive Dual-Washer Assembly
Both a plain washer and a spring washer are permanently retained under the head during manufacture, ensuring the correct washer combination is present at installation without any separate handling or placement by the assembler.
Cold-Forged Construction
Cold forging refines the grain structure of the stainless steel, typically producing consistent dimensional accuracy and good mechanical integrity across the screw shank and head compared with cut or machined alternatives.
Phillips Cross-Recess Drive
The Phillips recess accepts standard PH-series driver bits, making the screw compatible with both powered screwdrivers in production environments and hand tools during maintenance or field assembly operations.
Pan Head Profile
The low-profile pan head presents a wide, flat bearing underside that works in conjunction with the plain washer to spread clamping load, reducing the risk of surface indentation on softer or coated mating materials.
Metric Thread Compatibility
Standard metric threading across the M4 to M6 range ensures interchangeability with common metric tapped holes, insert threads, and nuts used throughout industrial panel and component assembly across multiple sectors.
Before you order
Diameter & Thread Engagement
Select M4, M5, or M6 based on the tapped hole or insert thread in the mating component. Confirm that thread pitch matches the mating part specification, and ensure adequate thread engagement depth is available in the parent material for reliable clamping.
Shank Length
Choose a shank length that achieves the required thread engagement without the tip protruding excessively into a clearance cavity or bottoming out in a blind hole. Length requirements should account for the combined thickness of all joined material layers plus any washer stack.
Grade Selection
SS 304 is generally adequate for indoor or mildly corrosive environments, while SS 316 may be more appropriate where chloride exposure, frequent chemical cleaning, or elevated humidity is anticipated. Discuss specific service conditions with the Accurate Fastners sales team if uncertain.
Quantity & Documentation
For production procurement, specify the required quantity and whether material test certificates or batch documentation are needed. Accurate Fastners' quality control team performs checks during procurement and delivery, so documentation requirements should be communicated clearly at the enquiry stage.
FAQs
Frequently asked questions
What does 'SEMS' mean and why does it matter for assembly?
SEMS refers to a screw supplied with one or more washers pre-assembled and captive beneath the head. This format reduces loose-part count at the assembly station, eliminates incorrect washer sequencing, and can simplify automated screwdriving processes by presenting a single feedable component.
Which material grades are available for this screw?
Accurate Fastners offers this Phillips pan SEMS screw in SS 304 and SS 316. SS 304 suits general indoor applications, while SS 316, with its molybdenum content, may offer better performance in environments with chloride exposure or aggressive cleaning agents.
What sizes are available?
The verified size range is M4 to M6 metric diameter. If you require specific length options or a size outside this range, please contact the Accurate Fastners sales team directly to confirm availability and lead times for your requirement.
Is this screw suitable for structural load-bearing joints?
This fastener is intended for panel attachment, cover fixing, and component mounting duties. It is not positioned as a structural tension fastener. For joints where load-bearing or safety-critical performance is required, please consult a qualified engineer and confirm suitability with the sales team.
Can I receive this screw with a plain washer only, without the spring washer?
The product as listed combines both a plain and a spring washer as captive elements. If you require a different washer configuration — such as plain washer only — please raise this with Accurate Fastners at the enquiry stage so the team can confirm whether alternative assemblies are available.
How do I request a quotation for this product?
You may submit an enquiry through the website enquiry form, send your specifications to export@accuratefastners.com, or contact the team via WhatsApp. Please include the required diameter, length, grade, quantity, and any documentation requirements to receive an accurate quote promptly.
Related Products
Complementary fasteners
- DIN 912304 · 316 · 202
DIN 912 Socket Head Cap Screw (Allen Cap Screw)
Size: M3 – M16
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