Founded in 1999, Interparts started out as a family business and continues that legacy today. The company focuses on servicing the larger bus companies in Europe with alternative product lines, such as slack adjusters, brake cams and air springs.

In 2008, the company developed a two-piece wheel nut indicator for a large bus company in the Midlands, and also extended its range of indicators for trucks and trailers. Today, the company is expanding with new employees joining from inside and outside the family. Interparts has positioned itself as a specialist in wheel nut loosening and as a company constantly developing new products.

The two-piece indicator it developed in 2008 was based on a rachet, such that after retorquing, the pointer could be reset in only an anticlockwise direction. For long-reach applications, the company developed a pointer with two small holes, just under the top and in line with the centre, such that cover would not trap moisture but would swing out due to centrifugal forces during service.

More developments were introduced, such as a pointer with retro-reflection material on top for the steering axle. Its design means that traffic in a vehicle’s blind spot will be warned by its reflection once the steering axle wheels are turning.

Back to the drawing board

In 2010, the company developed a polyamide retainer after a request from a bus company in London. This rigid device links two wheel nuts and does not allow any loose rotation of the wheel nuts, but could be tightened faster using a ratchet.

The company used its in-house-developed loosening machine – suitable for 22 mm studs – to test the retainer, producing positive results. Field tests with the London-based bus company took place over the next 18 months before the final test with vehicle testing company Mira snapped the strut after a few hours of fatigue testing.

Analysis of the failed stud showed that the additional stress was caused by the stud bending due to the relative movement of the hub and wheel. This created a stress level beyond the elasticity of the material and made the stud fatigue.

Interparts concluded that it was safer to develop a device that can accept a bit of loosening and indicate the loosening, but also prevents the play between wheel and hub. This play – when the wheel starts wobbling, is recognised as dangerous and the last stage before detachment.

Ever since, the company has developed two devices that accept a small angle of loosening, clearly indicating and preventing play between hub and wheel. The final development is the Twindicator, probably the next standard in wheel detachment prevention.

This product has all the benefits of the standard tag: multiples for precise fitting; 7 mm low to retorque while fitted; reusable; a melting warning when the brakes heat up; and it has the ability to prevent further loosening of the wheel nut, keeping it from entering the wobbling stage.

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