Every overlap seam on a hot-air jobsite comes down to one decision: which wide slot nozzle goes on the gun. Slot length sets how wide a heated band you lay down, and that number decides whether you finish a tarpaulin in one clean pass or chase a half-fused lap all afternoon. Here is how the three sizes we stock compare, from the Weissenberg Technical Team — 19+ years in plastic fabrication.
What a Wide Slot Nozzle Actually Does
It discharges a flat curtain of hot air instead of a focused stream, heating the top surface and the underside of both overlapped sheets at once. No filler rod is involved: once both surfaces reach fusion temperature, a silicone pressure roller consolidates them into a homogeneous joint as the material cools.
That is why these nozzles dominate overlap welding — PVC and TPO roofing membranes, tarpaulins and truck covers, awnings, banners and geomembrane patching. Nozzle choice here is engineering, not preference.
New to nozzle selection? Start with our plastic welding nozzle guide — it compares speed, wide slot and tubular nozzles — then come back here to pick your slot length.
The Three Sizes Side by Side
| Specification | 20 x 2 mm | 40 x 2 mm | 50 x 3 mm |
|---|---|---|---|
| Weldy article no. | 124.772 | 124.777 | 119.342 |
| Slot length (heated band) | 20 mm | 40 mm | 50 mm |
| Slot width (air curtain) | 2 mm | 2 mm | 3 mm |
| Nozzle connection | Ø 31.5 mm | Ø 31.5 mm | Ø 35.5 mm |
| Nozzle design | 15° angled, reinforced | 15° angled, reinforced | Straight, push-fit |
| Best fit for | Narrow laps, edges, parapets, patches | General membrane and tarpaulin work | Wide bands, long production runs |
20 x 2 mm — Narrow Laps, Edges and Detail Work
The Wide slot nozzle (Ø 31.5) 20 x 2 mm is the detail specialist. Its 20 mm band keeps heat concentrated where a full-width nozzle would spill over an edge, parapet, upstand or pipe collar — small repair patches, narrow reinforcing strips and trim work where a 40 mm band would overheat the surrounding membrane.
The 15° angled geometry matters here: it lets you hold the gun at a natural wrist angle while keeping the slot flat against the seam, so the band stays even in confined corners.
40 x 2 mm — The All-Round Membrane and Tarpaulin Size
If you keep only one wide slot nozzle in the toolbox, make it the Wide slot nozzle (Ø 31.5) 40 x 2 mm. The 40 x 2 mm size is a common choice for truck tarpaulins, awnings, banners, TPO/PVC roofing membranes, and pool or pond liners.
The 40 x 2 mm nozzle is the wider of the two wide-slot nozzles supplied in Weldy's Energy HT1600 and HT1600D overlap welding kits, alongside the 20 x 2 mm detail option.
50 x 3 mm — Wider Band, Ø 35.5 mm Connection
The Wide slot nozzle (Ø 35.5) 50 x 3 mm uses a different connection from the other two. Its 50 x 3 mm outlet produces a wider hot-air band than the 20 x 2 mm and 40 x 2 mm options, and because it uses a Ø 35.5 mm connection, tool compatibility should be confirmed before ordering.
Weldy currently lists the HG 330-A Universal Kit as a compatible product.
Angle and Roller Decide Weld Quality
Angle control. Keep the nozzle parallel to the seam. Tilt it and the leading edge of the slot starves while the trailing edge overheats the same lap.
The roller. The nozzle only heats; it does not press. The seam must be consolidated while still above softening temperature, so the roller follows immediately behind — a cold gap between heating and pressing is the classic cause of "zipper" failures. The 40 mm silicone pressure roller pairs with both the 20 mm and 40 mm nozzles.
Confirm the Weld Before You Run the Seam
Make a trial weld on offcuts of the actual material, then evaluate the result against the membrane manufacturer's instructions, the applicable welding procedure specification (WPS), and the project's acceptance criteria. Those documents — not a general rule of thumb — define the seam width, temperature and travel speed your job requires.
Ordering the Right Wide Slot Nozzle
Measure the nozzle seat on your gun — Ø 31.5 mm or Ø 35.5 mm — then choose slot length from the job. Every nozzle we ship is genuine Weldy tooling, backed by our 1-year warranty and lifetime technical support.
Browse the full Weissenberg Store accessories collection to compare wide slot, speed and tubular nozzles, or start with the hot air gun range if you are still choosing the tool. Not sure which slot length suits your material? Send us your membrane type, thickness and lap width and our team will tell you which nozzle to run.
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