The screw machine is practically the same as the turret lathe, but is used for different purposes; in fact, the screw machine when first designed had a turret, the tools of which were advanced in the proper order by means of levers and guide straps fastened to a guide drum. The screw machine is now built along the general lines of a lathe, but without a carriage. The tail-stock is replaced by a turret arranged to hold six or more tools, so that each one may be brought into play in the order in which it is needed, and each operation may be thus performed in its progressive order.

The latest machine of this class instead of permitting only one bar of stock at a time to be fed into the machine, and the tools advanced in order, allows five bars to be fed at once, five operations being performed at the same time. The only skill required to operate the machine is in the setting up of the tools and in the adjustment of the machine. The man who does this is not necessarily a machinist, but he must understand the screw machine and give close attention to the details of its operation.