The 90mm Connectors are the preferred method of connected bed frames with side rails greater than 100mm.  There are no bolts or nuts to tighten and the Joiners simply lock into place.  The mushroom shaped dome heads drop into the round hole with the shanks dropping down the curved slot to lock with the dome heads protruding.  Gravity and use of the bed will tighten the grip so that they won't come loose.  However for future storage or transport reasons the 90mm Connectors can be knocked apart quite easily.  The 4 flat Fixing Plates (with dome heads) are not 'handed' and can go in any corner and are usually fitted to the head rail and tail rail.  The 4 Angle Brackets are 'handed' in that there is a Left Hand pair and a Right Hand pair.  These are usually fitted to the side rails.  The large hole always goes to the top.  Lay out the 8 components in the desired position before commencing any assembly.  A hardware mechant will advise on the screw gauge, screw head size & type and length as this will vary depending on the construction of your bed frame.  28 screws are required in total for a set of 8 brackets.  A guide to the hole sizes and dimensions is shown under the Specifcations tab.