Which of the following is the most common drilling practice?

Drilling holes is considered the most common drilling practice because it is the fundamental method used to create circular holes in various materials, such as metals and plastics. This process involves the use of a rotating cutting tool called a drill bit that removes material from the workpiece as it penetrates. It is widely employed in manufacturing and machining operations for its versatility and efficiency, making it essential for producing holes for various applications, including fastening and assembly.

The other methods listed play specific roles in the machining process but are not as foundational as basic drilling. Counterboring is typically used to enlarge the entry of a pre-drilled hole to allow for a flat-bottomed recess. Reaming smooths and enlarges holes created by drilling to achieve tighter tolerances and improve surface finish. Lapping is a finishing process that involves removing material from a workpiece using an abrasive slurry but is not primarily used for creating holes. Therefore, while all these practices are important in machining, drilling holes stands out as the most prevalent and fundamental technique.