In my clinical experience, thyroid nodule of 5 mm or bigger merit further investigation as FNAB if there are 1 or 2 suspissous signs on ultrasonography.

I am agree, but we can´t forget risk factors such as thyroid patology (hashimoto or graves disease), gender, age and family history.

For all practical purposes ALL palpable nodules will need investigation. Nodules less than 1 Cm will be only seen on imaging. The investigation of small nodules will depend on the risk assessment  of a patient