Threaded lid SP40 red

SP40 threaded caps are protective caps in soft LDPE that are screwed onto external threads and protect them until the part is to be used. A damaged thread on a stud or a shaft journal is often discovered only at final assembly, and then it is expensive; a cap that costs next to nothing and stays on from machining to assembly is one of the cheapest insurances there is in the workshop.

The series covers 17 thread sizes from M8 to M52, with heights from 11 to 24.5 mm depending on the size. The caps are matte and signal red, which makes them easy to see both during inspection and when they are to be removed before assembly. You pick the thread size as a variant on the product page; dimensions per size are given in the manufacturer's data sheet.

The cap being threaded rather than pushed on makes a practical difference. A threaded cap stays on through handling, repacking and transport without shaking off, and it can be screwed on and off many times without losing its grip. LDPE is also a soft and tough material that springs against the thread flanks; it protects without damaging the thread itself, and it does not crack under normal handling even when the warehouse is cold.

The protection does its work in several stages. During transport and storage the cap keeps dirt, chips and moisture away from the thread and takes the knocks that would otherwise dent the outermost turns. During surface treatment it masks the thread; a cap screwed on lets you paint or blast the part without the thread having to be cleaned afterwards. Just check the temperature resistance before oven drying, since LDPE softens at relatively low temperatures and should not go into a hot curing oven.

Typical applications in Swedish industry: studs on engine and gearbox components that leave machining finished but are assembled later, threaded spigots on hydraulic parts, shaft ends with threaded journals in machine building, and spare parts that lie in stock for a long time and have to be ready to fit the day they are picked. Machine builders who deliver subassemblies to customers usually put caps on all exposed threads; it also looks well prepared at the goods inspection.

When choosing a size you start from the nominal size of the thread, so you pick the M16 cap for an M16 thread without further measuring. If you need to protect both external and internal threads on the same part, you add threaded plugs from the same family, which are available in matching versions. The red color at the same time works as a visual receipt in the assembly planning: as long as something red shows on the part, work remains.

The caps are reusable as long as the threads in the plastic are intact, which in practice means many cycles in internal handling between machining, stock and assembly. For one way deliveries to customers they can stay on as transport protection all the way.

The sizes above M30 make the series useful for coarser machine elements as well, which are otherwise hard to protect; threaded shaft ends on rollers and screw jacks often sit in exactly that range. And since the caps weigh a few grams each they affect neither freight nor handling, however many are fitted to the part. You can mix sizes freely in one order and still keep the number of items short, which purchasing tends to appreciate.

Do you want help working out the right sizes and quantities for your production? Get in touch with us.