Which of the following best describes mills in machining?

Mills in machining are versatile tools that can be made from solid metal or can accommodate indexable inserts, making option B the best description of them. This adaptability allows machinists to choose the appropriate cutting tool for the specific application or material being machined, enhancing efficiency and effectiveness.

Solid metal mills provide durability and can achieve high precision, while mills that use indexable inserts allow for quick changes to the cutting edge, thereby reducing downtime and improving productivity. This capability to employ various tools and methods is essential in modern machining practices where flexibility and efficiency are key.

The other options do not accurately represent the characteristics of mills. For example, single-point tools are typically associated with lathe operations, while milling tools often utilize multi-tooth cutters. Describing mills as solely for drilling overlooks their diverse applications, which include face milling, end milling, and slotting, among others. Lastly, while there are manual milling machines, many modern mills are CNC (Computer Numerical Control) machines, allowing for automated operations and enhancing consistency and precision.