Counter-bores are provided to ________

Explanation:

Counter Boring

• Counter boring is an operation of enlarging a hole to a given depth, to house heads of socket heads or cap screws with the help of a counter-bore tool.
• The tool used for counter-boring is called a counter-bore.
• Counter-bores will have two or more cutting edges.
• At the cutting end, a pilot is provided to guide the tool concentric to the previously drilled hole.
• The pilot also helps to avoid chattering while counterboring.
• Counterbores are available with solid pilots or with interchangeable pilots.
• The interchangeable pilot provides the flexibility of counterboring on different diameters of holes.
• Counterbore sizes are standardized for each diameter of screws as per BIS.
• There are two main types of counterbores. Type H and Type K.
• The type H counterbores are used for assemblies with slotted cheese heads, slotted pan heads, and cross-recessed pan head screws.
• The type K counterbores are used in assemblies with hexagonal socket head capscrews.
• For fitting different types of washers, the counterbore standards are different in Type H and Type K.