Abstract Symmet ric sw itches are usually used in the process of na rrow gaug e t ra nspo rtation o n tunnel const ruction si te. Refi t ting av ai lable sing le swi tch to symmet ric one ca n dispense w ith desig n a nd making w o rk. In this paper, a detailed method fo r refi t ting the sing le swi tch to symmet ric one i s presented.
1997, Vol. 14 
