Salient Features of Double Tube Rheostats :- 1) Core Porcelain Tube, Non-Magnetic Non-Inductive Tubular Type. Diameter and Length of coreis given in the table below. 2) Contact Block : Squire piece made of material is fitted with contact sliders in the guide squir rod. Bright chrome plated Phosphor bronze strip which makes immediate contact with the guide rod. A backlite knob is fitted with squire piece for sliding up and down. 3) Guide Rod : Solid draven brass rod bright chrome plated squire. 4) Contact Material : Multiple brushes of Phosphors bronze strip rolled strip give springy action to the contacts.