This study experimentally investigated the effects of joint specifications and surface treatment methods of countersunk parts on the slip resistance of single-surface frictional joints using countersunk high-strength bolts with a head opening angle of 92◦. The results showed that the slip coefficient of countersunk bolts was higher than that of high-strength hexagonal bolts, and the slip coefficient remained unchanged even when rust-proof painting was applied to the countersunk parts. Additionally, it was found that using enlarged holes improved the slip coefficient by 3% to 7%. Furthermore, there was a tendency for the slip coefficient to decrease and its variation to increase when the slip-to-yield strength ratio was high.
