8) Which has an exterior pipe thread end and used for fitting in the socket?

9) What is the name of joint that has threads on both sides of the central piece?

10) How much gap is allowed from the end of pipe after 15 Degree chamfering in ring seal joint?

11) What is the size of trench width for PVC pipes?

12) Which is the material on trenches for PVC pipes are laid over it?