Three-spoke knob R53 bushing black

Three-spoke knobs R53 with a bushing are locking knobs in polyamide PA6, shaped so the hand can apply real tightening torque without slipping. The three spokes give the fingers defined contact faces all the way around the knob; compared with a knurled round knob less hand force is needed for the same torque, and that shows at the end of a shift. The thread sits in a threaded hole in a brass bushing, so the knob is fitted onto a stud or screw and works as a nut.

The series covers eight versions with the diameters 45, 65, 85 and 105 mm and the threads M8, M10 and M12. The thread depth varies with size and thread, from 10 up to 22 mm, and the height goes from 21 to 45 mm. All versions are black with a matte surface and are picked directly on the product page under the same item.

PA6 is an obvious material choice for hand operated clamping elements. It is tough, takes knocks and point loads without cracking and feels pleasant in the hand even in cold premises. The brass bushing gives a smooth thread run against the steel bolt that does not seize or wear with daily use; a thread straight in plastic would have gone slack considerably faster in a fixture that is reclamped every hour.

The natural home of the knob is the clamping fixture: clamping work pieces on drilling and milling tables, locking adjustable stops, clamping tool parts and mounting positions on welding tables. Outside the workshop the same knob turns up on jigs in the furniture industry, on test equipment in laboratories and on adjustable machine guards; everywhere somebody clamps and releases by hand several times a day.

The choice of diameter follows the torque needed. A 45 mm knob suits M8 joints that are mostly there to fix a position, while the 105 mm knob with M12 clamps with a force that would otherwise have called for a tool. Choose one size larger if the operator works with gloves; the extra leverage costs a little space but saves both time and wrists. Full dimensions for each version are in the manufacturer's data sheet.

A practical tip for sensitive surfaces: combine the knob with a pressure plate between the end of the thread and the material, for example a plate in polyethylene for M8. The plate spreads the clamping force over a larger area and stops the screw end from marking painted or anodized parts when the knob is tightened. In fixtures that clamp straight against finished surfaces it is cheap insurance.

Ordinary rules for threaded joints apply when fitting: check that the bolt does not bottom out in the bushing before the knob sits against the face, and use a lock nut if the joint vibrates. The knobs are supplied in packs of 75 to 200 pieces depending on size, so the series works just as well for one off fixture builds as for product design in volume.

The ergonomics can be argued with more than comfort. Repetitive clamping work with poor grips is a known source of strain problems in hand and forearm, and a knob that lets the operator apply the torque with an open hand instead of a cramp in the fingertips makes a real difference over a working year. Safety representatives and production engineers tend to agree on that; it is cheaper to pick the right knob from the start than to deal with the trouble afterward. The shape of the grip is therefore not a matter of style but a specification.

Do you have a fixture where the knob is to sit? Get in touch and we will help you find the right size and thread.