Counterbores Spec Table
2 types of spec data
Counterboring and countersinking create recesses so that bolt heads or nuts sit flush with or below the part surface. Counterbores (cylindrical) suit socket head cap screws; countersinks (conical) suit flat-head screws. Both are standardized per KS/ISO for each bolt nominal size. Counterbore depth equals the bolt head height plus 0.5–1mm clearance.
Frequently Asked Questions
What is the difference between a counterbore and a countersink?
A counterbore is a cylindrical recess for socket head cap screws to sit below the surface. A countersink is a conical recess (typically 90°) for flat-head bolts to sit flush. Both achieve a flush surface finish.
How is counterbore depth determined?
It must be at least the bolt head height. Typically bolt head height + 0.5–1mm clearance. KS/ISO spec tables list recommended counterbore diameter and depth for each bolt size.