Overview
When shopping for vertical window seals and roll-up quarter window seals, you'll notice similar part numbers with different suffixes—like VS 3 versus VS 3-M. Understanding the difference helps you choose the right product for your application and ensures a professional-quality seal.
The Two Types of Construction
| Feature | Rubber Extrusion Only (e.g., VS 3) | Steel Core / Molded (e.g., VS 3-M) |
|---|---|---|
| Construction | Solid rubber with no internal support | Galvanized steel core fully encased in rubber |
| Rigidity | Flexible—can bend or sag over time | Rigid—maintains shape permanently |
| Best For | Horizontal applications, repairs | Vertical seals (quarter windows, division bars) |
| Installation Difficulty | More challenging on verticals | Easier—holds position during installation |
| Sealing Performance | Good | Superior—steel core prevents gapping |
When to Choose Steel Core (The "-M" Suffix)
For any vertical application, we strongly recommend the steel core version. Here's why:
- Gravity Works Against Rubber-Only Seals On vertical window channels, a rubber-only extrusion can slowly stretch or sag under its own weight. The steel core acts as an internal "spine" that prevents this deformation.
- Superior Sealing Pressure The steel core stiffener allows the rubber to maintain consistent pressure against the glass as it rolls up and down. This eliminates gaps that cause wind noise and water leaks.
- Easier Installation Steel core seals hold their shape while you work, making them easier to position correctly. Rubber-only extrusions tend to twist or bunch up during installation.
- Longer Service Life Metro uses only galvanized, corrosion-resistant steel cores that won't rust inside the rubber. Combined with our SUPERsoft rubber compound, steel core seals typically outlast rubber-only versions.
When Rubber-Only Extrusion is Acceptable
Rubber extrusion without a steel core works well for:
- Horizontal applications (trunk seals, door bottom seals)
- Curved sections where flexibility is required
- Repairs where you need to splice or join sections
- Universal applications where exact length is cut from bulk rolls
Quick Reference: Common Part Number Patterns
| Suffix | Meaning | Example |
|---|---|---|
| (No suffix) | Rubber extrusion only | VS 3 |
| -M | Molded with steel core | VS 3-M |
| -Q | Quarter window specific molding | VS 3-Q |
| -O | OEM profile match | VS 3-O |
Pro Tip: Adhesive Still Matters
Even with the superior rigidity of steel core seals, we recommend using 3M Black Weatherstrip Adhesive (GL-11) at critical points—especially at the top and bottom ends of vertical seals where lifting can occur over time.
Bottom Line: If the seal runs vertically on your vehicle, choose the steel core version. It's worth the modest price difference for dramatically better performance and easier installation.