Back-gear mechanism is provided in cone pulley headstock to

Increase the speed and reduce the feed

To face the workpiece up to the end of the centre hole

A lathe half centre is used to face the workpiece up to the end of the centre hole.

Cast iron

Cast iron is commonly used for machinery housings or base due to its damping characteristics. It is also known for holding its shape when it is subjected to contraction and expansion due to temperature fluctuations. Hence lathe bed is usually made up of cast iron.

Threading chaser

Threading chaser is used for finishing and maintaining correct form of thread.