The ceramic knobs are the type that consist of two pieces with a nail running through the middle. They were nailed directly into the wall studs or floor joists. Electrical wires were wrapped around the knob, which securely anchored them. The knobs separated the wire from potentially combustible framework. Because they were suspended in air, they could dissipate heat well. They also facilitated changes in direction and ensured that wires were not subject to excessive tension. The ceramic tubes were inserted into holes bored in wall studs or floor joists, and the wires were directed through them. This kept the wires from coming into contact with the wood framing and from being compressed by the wood as the house settled. There is a great deal of integrity to this old method of wiring. As my electrician pointed out, knob and tube wiring is in some ways superior to today's wiring, (except for some flaws such as lack of a ground conductor). And most noticeably, today's wiring won't offer up any timeless ceramic when it is replaced a century from now.