1. How to distinguish plastic switch between bakelite switch?
   Answer: Burn bu the lighter, plastic switch will melt, but bakelite switch will not. Because bakelite with excellent heat-resisting. Look at their surface, plastic one lighter than balelite one.

 2. Why bakelite switch better than plastic Switch?
    Answer: Because bakelite switch with high mechanical, excellence insulativity, heat-resisting, corrosion-resisting. The property of plastic is more inferior than bakelite, plastic switch with conducting possible, easy to lose efficacy.

 3. How to distinguish copper wire between aluminum wire?
   Answer: Look at their surface can not find their difference. But when you twist both them, aluminum will broken but copper wire will not. Because aluminum with poor fatigue resistance,fracture easier than copper wire.

4. Why using aluminum wire motor is cheaper?
   Answer: Because aluminum is cheaper than copper, besides, aluminum wire is not stable.

5.Compare round cast iron motor housing and  round wrought iron crust motor housing, which one is bettter?  
Answer: Round cast iron motor housing is better, this motor housing with high concentricity, good heat dissipation and simply maintenance.