Description
A 3.95 mm by 38 mm fastener with a Ruspert multi-layer coating and a conical countersinking head is what the NoMorePly render carrier board guide asks for on timber framework — supplied 250 to a box, enough for roughly nine full 2400 x 1200 mm sheets at 600 mm batten centres.
Where STS Render Board Screws Fit on a Carrier-Board Facade
STS render board screws are the 3.95 mm by 38 mm fastener that the NoMorePly render carrier board guide recommends for fixing 12 mm fibre-cement board to timber framework, driven flush before basecoat and mesh. That written recommendation is why Renders World stocks them inside the rendering cement boards range rather than leaving the fastener to whatever is in the van.
The board itself is specified for timber frame, lightweight steel frame and modular or offsite construction, and it always sits on battens over a vented cavity. The screw's job is the board-to-batten connection in that build-up, so the settings it covers follow the batten, not the wall behind it.
- Timber-framed and offsite construction: boards fixed to vertical battens of minimum 25 x 60 mm at 600 mm centres, or 400 mm centres where the elevation carries higher wind load or exposure.
- Over-boarding an existing substrate: the same schedule applies, with the battens themselves fixed firmly through to the structural frame behind.
- SIP panels: the guide treats the outer OSB layer as structural enough to take the batten framework directly, battened out vertically at 400 mm or 600 mm centres.
- Light-gauge steel framing: the guide names a different fastener here — a 4.8 x 38 mm wingtip self-drilling screw — so steel-frame work is specified separately rather than covered by this box.
Why Installers Specify the Ruspert-Coated 38 mm Board Screw
- A coating built in layers, not plated on: the datasheet describes a free zinc layer in contact with the base metal giving sacrificial protection, a chemical conversion layer above it, and a baked ceramic topcoat acting as the physical barrier. The conversion layer is what stops the ceramic and zinc separating under abrasion.
- Classified corrosion performance: Ruspert grades are set by hours in neutral salt spray before red rust appears, and all STS Ruspert products are stated as R1000 or R1500. Specify against the R1000 floor — 1000 hours to red rust, comparable to a class 3 screw for mild to moderate industrial or marine exposure.
- Alkaline resistance where it matters: the ceramic layer is described as protecting the zinc and substrate from both acid and alkaline attack, which is the exposure a fastener meets in the damp, high-pH zone behind a cement basecoat.
- Conical head for a flush countersink: the 7 mm head pulls level with the board face, leaving the flat plane that basecoat and mesh need so no head reads through the finished topcoat.
- Treated timber and impact drivers: the sheet lists compatibility with treated hardwood and softwood among the coating's benefits, and confirms the screw is suitable for use with an impact driver — which is what most installers will actually reach for.
Technical Specification, Read From the STS Datasheet
| Property | Value |
|---|---|
| Manufacturer product name | External Render Board Screw |
| STS product SKU | 5638 |
| Length | 38 mm |
| Major diameter, threads | 3.95 mm |
| Head style | Flat, conical countersink |
| Head diameter | 7 mm |
| Drive and recess | Phillips |
| Drilling width | 3.52 mm |
| Coating | Ruspert multi-layer, ceramic topcoat |
| Corrosion grade, STS Ruspert range | R1000 or R1500 |
| Board compatibility | 12 mm fibre-cement board |
| Box quantity | 250 |
| Price | £12.50 per 250-piece box, Aug 2026 |
Two dimensions that circulate for this screw are left out above on purpose. The shank diameter and the recess depth sit in a datasheet table whose labels and values cannot be paired with confidence, and the neighbouring NoMorePly screw sheet gives different figures again for both — so if a specification demands either dimension, ask STS to confirm it against SKU 5638 rather than lifting it from a distributor listing.
How to Install: Batten Centres, Edge Distance and Fixing Counts
Fixing counts come from the board guide rather than a rule of thumb, and they are quoted per full sheet at each batten spacing. Setting the schedule out before the first board goes up is what keeps the elevation consistent from ground to eaves.
| Batten centres | Fixings per 2400 x 1200 mm sheet | Orientation |
|---|---|---|
| 400 mm | 28 | Horizontal or vertical |
| 600 mm | 27 | Horizontal |
Hold fixings 20 mm in from board edges as the guide recommends; STS also report having tested successfully at 15 mm, so treat 20 mm as the working figure and 15 mm as the tested limit when a cut piece leaves you no choice. Leave the specified 3–5 mm gap on all sides of every board, which is what absorbs timber movement before it reaches the mesh layer.
Set the depth stop on the driver against an offcut before starting the elevation proper, and every head lands at the same plane across the wall. Fill the joints with the basecoat mix where render follows soon after boarding — the same EPS adhesives basecoats range supplies the mesh-embedding coat that goes over the fixed boards, ahead of primer and the thin-coat silicone render finish the guide illustrates as the typical build-up.
Two cavity details are worth carrying into the specification, because they change by nation. The cavity must be vented top and bottom with a minimum 15 mm airflow gap, and while a 60 x 25 mm batten satisfies England and Wales, the guide sets a minimum 50 mm cavity depth for Scotland, Northern Ireland and the Republic of Ireland. The cement board installation guide works through the full sequence, and the timber frame moisture and airtightness notes cover why that vented cavity earns its place.
How Many Boxes to Order for Your Board Count
Because the fixing count per sheet is published, a box of STS render board screws converts cleanly into board area. Both figures below use the full 2400 x 1200 mm sheet at 2.88 m², and round down to whole sheets so the last board on the pallet is never short.
- At 600 mm centres: 250 ÷ 27 fixings per sheet = 9.2, taken down to 9 whole sheets; 9 x 2.88 m² = 25.9 m² of board per box.
- At 400 mm centres: 250 ÷ 28 = 8.9, taken down to 8 whole sheets; 8 x 2.88 m² = 23.0 m² per box.
- Cost basis: £12.50 ÷ 250 = £0.05 per screw, and £12.50 ÷ 25.9 m² = about £0.48 per m² of board at 600 mm centres.
- Half-size boards: the guide publishes fixing counts only for the full sheet, so quantities for the 1200 x 800 mm board are set on site from the same perimeter and intermediate pattern rather than from a published figure.
Add a box for offcuts and replacements on any elevation with a lot of openings, since cut pieces need their own perimeter fixings. Renders World lists the 250-piece box as available at the time of this August 2026 check.
Ruspert or Zinc-Plated: Checking the Right 38 mm Screw
Two 38 mm screws sit close together under the STS render board screws name, and the boxes look similar on a shelf. The external screw is SKU 5638, Ruspert coated, 250 to a box; the internal fibre-cement board screw is SKU 5647, zinc plated, 200 to a box, and its own datasheet positions it for wet areas such as bathrooms, wet rooms and kitchens. Count the box and read the coating — that is the whole check.
- External render on a carrier board, timber framework: this box. Ruspert coating, conical flush head, and the 3.95 x 38 mm size the guide names for timber.
- Light-gauge steel framing: specify the 4.8 x 38 mm wingtip type the guide calls for on SFS instead, and confirm the fastener is stainless or suitably treated for external use.
- Internal wet-room and tile-backer work: the zinc-plated 200-piece screw is the one carrying that recommendation, not the Ruspert external screw.
- Fixing insulation rather than board: EPS, graphite EPS and mineral wool take mechanical plugs and base tracks, which the insulation fixing accessories range covers.
- Ready to order: match one box to nine full sheets at 600 mm centres and add the 2.4 m x 1.2 m STS carrier board to the same delivery so the fixings arrive with the boards they belong to.
FAQ — Fixing Counts, Frame Type and Coating
How many screws does a full board take?
The guide gives 27 fixings per 2400 x 1200 mm sheet on battens at 600 mm centres, and 28 per sheet at 400 mm centres. A 250-piece box therefore covers nine full sheets at the wider spacing and eight at the closer one, once rounded down to whole boards.
Can these screws fix boards to steel framing?
For all SFS framing the board guide recommends a 4.8 x 38 mm self-drilling, self-countersinking wingtip fixing rather than the 3.95 mm timber screw, with the fastener stainless or suitably treated and approved for external use. Confirming the frame type at survey keeps the right fastener in the specification from the start.
How close to a board edge can the screws go?
STS recommend fixing 20 mm in from edges, and report having successfully tested fixings at 15 mm from the edge. Working to 20 mm as standard leaves the tested 15 mm in reserve for cut pieces around openings.
What corrosion grade does the Ruspert coating carry?
All STS products with Ruspert coating are stated as R1000 or R1500 grade, classified by hours in neutral salt spray before red rust appears. An R1000 coating also conforms to 12–15 cycles of the DIN 50018 sulphur dioxide gas corrosion test, comparable to a class 3 screw for mild to moderate industrial or marine environments. The datasheet does not tie SKU 5638 to one of the two grades, so specify against R1000 as the floor.
How should boxes be stored on site?
Keep boxes closed and dry in the compound, on a shelf rather than the floor. It is ordinary good practice with any coated fastener and takes nothing more than a lid and a dry shelf.
Technical Documentation