Metal Roofing Screw Size Chart: Gauge, Length, Drill Point & EPDM Washer Guide
Think picking the right metal roofing screw is just about grabbing the longest one in the box? Think again.
Over 11 years of supplying roofing fasteners to export markets, we’ve seen more installation leaks and failures from wrong sizing than from poor material quality. If you don’t use the right screw for your roof panel profile, supporting substrate, material thickness, and weather sealing requirements, you will get a callback
This guide breaks down how to read screw sizes, pick the right length and drill point, and specify EPDM washers correctly. We provide self-drilling roofing screws in bulk to roofing contractors, hardware distributors, project buyers, and importers.
Quick Selection Checklist
Run through this checklist before you send an inquiry or place an order. It cuts quotation time in half and avoids 90% of the most common ordering mistakes we see:
●Roof panel material and thickness
●Steel purlin, timber, or other supporting substrate
●Total thickness of all metal layers in the drilling path
●Required screw diameter and length
●Drill point type and drilling capacity
●Head style and drive size
●EPDM washer specification
●Coating, corrosion-resistance requirement, and color
●Packing quantity and private-label requirements
Pro tip: Always note the actual diameter in mm on your purchase order, not just the gauge number. We’ll cover why next.
A correct screw specification reduces installation problems such as point burn-out, stripped threads, damaged washers, and water leakage around the fastening point.
How to Read a Metal Roofing Screw Size
Here’s the number one ordering mistake we fix every single week: buyers only put a gauge number on their PO. Gauge systems vary by region and factory, and it’s an easy way to end up with the wrong diameter.
Metal roofing screws are sized in either metric or imperial format:
A metric size such as 5.5 × 65 mm normally identifies:
●5.5 mm: nominal screw diameter
●65 mm: nominal screw length
An imperial size such as #12-14 × 2 in. normally identifies:
●#12: nominal screw diameter
●14: threads per inch
●2 in.: nominal screw length
Always cross-check against the product drawing before you finalize an order. Gauge labels aren’t universal – a #12 from one factory can be 5.2mm, and 5.5mm from another. Putting the exact mm diameter on your PO eliminates this risk entirely.
Metal Roofing Screw Size Chart
The chart below covers our standard stocked hex-head self-drilling roofing screw sizes. Custom lengths and diameters are available for OEM orders, but these are the sizes we keep on hand for 7-day lead times.
| Nominal Diameter | Common Lengths Available |
| 4.2 mm | 13, 16, 19, 25, 32, 38 mm |
| 4.8 mm | 13, 16, 19, 25, 32, 38, 45, 50 mm |
| 5.5 mm | 19, 25, 32, 38, 41, 50, 63, 75, 80, 90, 100, 115, 125, 135, 150, 165, 185 mm |
| 6.3 mm | 19, 25, 32, 38, 41, 50, 63, 75, 80, 90, 100, 115, 125, 135, 150, 165, 185 mm |
Note: 5.5mm and 6.3mm diameters are our highest-volume export sizes for North America, Australia, and Southeast Asia. We keep roughly 2.4 million pieces of each in stock year-round.
Important: This chart is for quotation reference only, not structural design. Bigger isn’t always better – the right size is the one that matches your exact roof build-up. Always confirm final specs with your project engineer.
How to Choose the Right Roofing Screw Length
Screw length is one of the most commonly mis-specified specs. You can’t just go by the visible roof sheet – you have to account for every layer in the build-up.
For a standard installation, you need to account for:
●Metal roofing panel thickness
●Washer and head seat depth
●Any insulation, spacers, or air gaps between layers
●Steel purlin or timber support thickness
●Minimum required thread engagement in the base material
Quick rule of thumb for steel purlins:
add 10–15mm to your total material thickness to get the minimum screw length. For timber, add 20–25mm.
From our in-house pull-out testing, a screw that’s only 5mm too short will fail load testing 3 out of 5 times. It’s not a risk worth taking.
On the flip side, going longer than you need drives up cost, slows down installation, and can cause issues with interior clearance on low-profile roofs.
Different connection points also need different lengths – here’s what to focus on for each:
| Application | Main Selection Consideration |
| Metal panel to steel purlin | Total steel thickness and drill point capacity |
| Metal panel to timber | Timber depth, thread design, and penetration requirement |
| Sheet overlap or stitching connection | Number of sheet layers and required sealing position |
| Flashings, ridge caps, and trims | Profile height, layer build-up, and substrate location |
| Insulated roof or sandwich panel | Panel thickness, support material, and fastening system requirement |
Do not select a roofing screw only by copying the size used on another project. A change in panel profile, purlin thickness, insulation thickness, or coating requirement can change the correct specification.
Why Drill Point Selection Matters
Drill point is the single most overlooked part of a roofing screw spec – and the number one cause of burnt-out points and slow installation on site.
Here’s how it works: the drill point has to cut through all steel layers before the threads engage. If the point can’t handle the total thickness, it overheats, breaks, or strips the thread.
Last quarter, a client in Queensland had to pause a 5,000m² roof project because their screws kept burning out halfway in. Turns out they were using a #3 drill point (rated for 4mm max steel) on 6mm thick purlins. A switch to #5 points fixed the issue within 3 days.
Remember: you’re sizing the drill point for the total steel thickness, not just the top sheet. That includes the roof panel, any intermediate steel layers, and the purlin or support.
Before you order, ask your supplier to confirm:
●Maximum total drilling thickness for the point
●Compatible base materials (steel, timber, etc.)
●Recommended point type for your build-up
●Suggested screw gun torque settings
●Independent test data for drilling performance
The drill flute must remain clear long enough to remove metal chips during installation. If the point is not suitable for the steel thickness, the screw may drill slowly, overheat, break, or fail to create a reliable thread.
EPDM Washer: The Seal Around Every Roofing Screw
Even the best screw will leak if the washer fails. It’s the most critical part for weatherproofing, yet many buyers treat it as an afterthought.
For exposed roof fasteners, a bonded EPDM washer with a metal backing is standard – it creates a tight, weather-resistant seal around the penetration point.
Here’s a common myth: thicker EPDM washers seal better. That’s not always true. For thin 0.4–0.7mm roof sheets, a 3mm thick washer won’t compress evenly, and you’ll end up with tiny gaps around the edge. For most standard panels, 1.5mm EPDM is the sweet spot.
For proper installation:
●Under-driven = washer not fully compressed = potential leaks
●Correctly driven = washer compresses evenly, no distortion = full seal
●Over-driven = washer deforms, coating damages = lost sealing performance
One more thing: the screw has to go in perfectly perpendicular. Drive it at an angle, and you’ll get an uneven seal even if the washer looks fully compressed.
For projects in humid, coastal, high-UV, or highly corrosive environments, the washer, coating, screw material, and roof panel material should be reviewed as one system. Do not select the fastener only by color or unit price.
Coating and Corrosion Protection
Coating is where a lot of buyers cut costs – and regret it 2–3 years down the line when rust spots start appearing.
Roofing screws come with zinc plating, painted finishes, organic coating systems, or full stainless steel, depending on your environment.
Before ordering, confirm:
●Indoor or outdoor use
●Coastal, industrial, or high-humidity exposure
●Compatibility with the roof panel material
●Required color match
●Required corrosion test standard or project specification
●Expected service conditions
For reference, our standard painted roofing screws pass 1,000 hours of neutral salt spray testing without red rust. Many budget suppliers only guarantee 200 hours.
A painted head may match the roof panel, but color alone does not define corrosion resistance. Ask for the coating description, technical documentation, and any project-specific compliance requirement before approval.
5 Screw Sizing Mistakes We See Every Month (And How To Avoid Them)
Only measuring the visible roof sheet This is the most common mistake. Buyers measure the 0.5mm top panel and order a drill point rated for 1mm – then it can’t get through the 3mm steel purlin underneath. Always size for the full steel build-up.
Confusing gauge number with actual diameter Gauge systems aren’t standardized across factories or regions. Always put the exact mm diameter on your purchase order to eliminate shipping errors.
Using the same screw for every connection point Panel-to-purlin, sheet overlap, flashing, ridge cap, and sandwich panel connections all need different lengths, drill points, or thread designs. One size does not fit all.
Ignoring washer installation quality A premium EPDM washer won’t fix an over-driven screw, angled installation, or damaged panel coating. Installation quality matters as much as the fastener itself.
Sending a vague inquiry for quotation “Roofing screws” is not enough info for an accurate quote. A proper inquiry includes size, point type, washer, coating, color, packing, and intended application.
Metal Roofing Screw Specification Checklist for Buyers
Use this checklist when you request samples or a quotation. It makes sure we have all the info we need to give you an accurate price and lead time on the first try:
●Screw size: diameter × length
●Head style: hex washer head, hex flange head, or other required design
●Drive size: confirm matching socket or driver bit
●Drill point: selected for the total thickness of the substrate
●Thread type: suitable for steel, timber, or the specified joint
●Washer: bonded EPDM washer and metal backing washer requirement
●Coating: zinc, painted finish, corrosion-resistant coating, or stainless steel
●Color: roof-panel color reference if required
●Application: panel-to-purlin, panel-to-timber, stitching, flashing, or repair
●Packing: box quantity, carton quantity, private label, barcode, or retail packaging
●Documentation: product drawing, inspection requirement, and sample approval process
Frequently Asked Questions
What size screw should be used for a metal roof?
There’s no one-size-fits-all answer, but for most standard 0.5mm steel panels on 3mm steel purlins, 5.5 x 32mm with a #3 drill point is our most commonly recommended spec. Ultimately, the right size depends on your panel profile, substrate, total layer thickness, and fastening location. Always treat diameter, length, drill point, washer, and coating as one complete system.
How long should metal roofing screws be?
Long enough to pass through every layer and get full thread engagement in the support material. As a rough guide, add 10–15mm to your total steel thickness for purlin connections, and 20–25mm for timber. Always follow the roof system manufacturer’s spec – don’t just pick a length by how it looks.
Do metal roofing screws need EPDM washers?
For exposed fasteners that penetrate a roof panel, a bonded EPDM washer is commonly used to help seal the penetration point. The washer must be installed evenly and must not be over-compressed.
Can one self-drilling screw be used for every steel thickness?
No, absolutely not. Drill points are engineered for specific thickness ranges. Use a point rated too thin, and it’ll burn out or break. Use one rated too thick, and it won’t form a clean thread in thin material. Always cross-check your total steel thickness against the manufacturer’s drilling capacity chart.
Is a larger screw always stronger?
Not necessarily. Screw diameter, length, point, thread, substrate, coating, and installation quality all affect the final connection. The correct fastener is the one that matches the roof system specification.
Get A Precise Screw Specification For Your Project
For an accurate quote in 24 hours, send us your roof panel type, support material, total steel thickness, required screw specs, coating requirements, color, and packing details.
At Sinsun, we help contractors, distributors, and importers put together clear, error-free screw specifications for samples, bulk orders, private label packaging, and export projects. Getting the spec right before production is the simplest way to avoid installation headaches and costly delays down the line.
We also offer free pre-production samples for testing – just ask when you reach out.