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PUSH-ON FRICTION-FIT KNOBS

The simplest fixing of all: no screw, no collet – just a knob bore sized to grip the spindle by friction or a light interference fit, sometimes assisted by internal ribs or a serrated bore that bite slightly into the shaft surface. Assembly is a single push, front of panel, with no tool at all.

The appeal is obvious. It’s the lowest-cost option per unit, the fastest to assemble by hand or by automated pick-and-place, and there’s nothing to loosen off internally over time in the sense of a screw backing out. Push-on fixing also suits knobs that are genuinely never meant to come off again, such as sealed consumer appliance controls.

The limitation is equally obvious once you think about torque and tolerance. Retention depends entirely on tightness of fit, so it’s sensitive to moulding tolerance stack-up, to thermal expansion differences between the plastic knob and a metal spindle, and to repeated removal and refitting – all of which reduce grip over time.

Push-on fixing is not the choice for a knob that will see frequent adjustment under load, high ambient temperature swings, or any application where the knob coming loose has a safety or performance consequence. It’s also not ideal for indexed or pointer knobs on splined shafts if the marking has to land in exactly the same rotational position every time it’s fitted (though this is not an issue if the potentiometer has a flattened D-shaft and the knob pointer is designed to take account of this).

Where to use it: low-cost consumer electronics, single-fit assemblies with no expected rework, and simple rotary switches or basic level controls where precise torque capacity and long-term retention under stress are not the priority.