28.—In the case of any machine in a factory being a machine intended to be driven by mechanical power—
(a) every set-screw, bolt or key on any revolving shaft, spindle, wheel or pinion shall be so sunk, encased or otherwise effectively guarded as to prevent danger,
(b) all spur and other toothed or friction gearing, which does not require frequent adjustment while in motion, shall be completely encased unless it is so situated as to be as safe as it would be if completely encased.
