Conical plugs SP35 red

Tapered plugs SP35 are protective plugs in soft LDPE that close off, keep dirt and paint out and protect sensitive surfaces during transport, storage, surface finishing and assembly. Thanks to the tapered shape the same plug works in two directions: it can be pushed into a hole or a tube end as a plug, or slipped over a stud, a threaded end or a tube as a cap. The plugs come from a Swedish maker of machine elements and are a standard choice in the engineering industry.

The range of sizes is what makes the series genuinely useful. SP35 comes in more than a hundred sizes, from plugs for holes under 5 mm up to sizes around 320 mm; that covers everything from a small threaded hole in a valve block to large tube ends and flange openings. Each size is given with two dimensions, and the taper means that every single plug also suits a small span of hole diameters. You pick the size as a variant on the product page.

The material is LDPE, a soft and yielding polyethylene. The plug gives just enough to shape itself against the edge of the hole and close tight without tools, but springs back and stays put by its own tension. LDPE stands up to water, oils and most of the common chemicals in a workshop, and the plug can be reused many times before it is worn out.

Inside and outside mounting place different demands, and the tapered shape handles both. As a plug it bears against the edge of the hole with its taper and the wider end stays outside as a stop and a grip surface; as a cap the taper grips around the outside of the stud or the tube instead. One and the same item can therefore replace both plugs and caps in many cases, which simplifies both purchasing and the store.

The red color is chosen on purpose. A protective plug only does its job if it is also removed at the right moment, and a bright red plug is hard to miss at final inspection; forgotten plugs in oil and hydraulic connections are a classic and expensive assembly mistake. Red also shows up well in a scrap bin, so reusable plugs get found instead of thrown away.

Typical uses: protection of threads and machined surfaces during handling, painting and transport, closing off hydraulic and pneumatic connections before commissioning, dust protection on tube ends during construction, and sealing of openings that are to stand empty until the next stage. In wet painting the plugs work as masking for holes that have to be kept free of paint.

Picking the right size is easy with a caliper in hand. Measure the diameter of the hole for inside use, or the outside diameter of the stud or tube for outside use, and pick the plug whose span of dimensions is closest. If the plug sits too loose, go up one size; the tapered shape means it only creeps further in before it stops. The height varies between the sizes, typically from around 5 mm on the smallest up to 40 mm on the largest, so even deep holes get a proper grip.

For recurring needs it pays to go through which hole sizes actually turn up in production and set up a small stock of those sizes; plugs are one of those parts that are always needed urgently and rarely at hand.

Measure the hole and compare with the list of dimensions. If you cannot find a size that matches, contact us and we will look further in the series.