Surface Bolts are secured to the door using screws whilst flush bolts are morticed into the door itself. Both kinds of bolts can help provide additional security to your door and the bolts slide into a strike or receiver plate.
Surface bolts are easier to install and leave minimal damage to a door since they do not require mortising and they can also be used on windows or gates for this reason.
Flush bolts however, give a nice discreet look and are usually used at the meeting point of a pair of rebated doors. Not only does their concealed nature make them aesthetically pleasing, but as they are hidden when the door is closed, this makes them extra secure.
Surface and flush bolts are available in a wide range of designs, finishes and sizes.