The AOM replacement bridge is supplied with two studs that fit in place of the existing AOM bridge mounts. The contact surface is a spherical shape and there is a matching shape in the end of the bridge support posts. When the bridge is mounted it can pivot on the studs so that it can rock back and forth with the movement of the tremolo.
There is a spiggot on the stud that locates in a hole in the mounting posts. On the rocking version the spiggot is smaller than the hole so that it will allow the bridge to rock back and forth with the tremolo movement, just like the standard Fender vintage style bridge.
On the non rocking version the spiggot is the same size as the hole so that it restricts any movement.
When ordering it is recommended that you select the 'rocking' version if you intend using the tremolo and the 'non rocking' version if you will not be using the tremolo.