One type of Trembucker that we made famous is our patented Parallel Axis design [see]. Here, four pole pieces per string insure that all the vibrations are captured for greater tonal range and dynamics. Because they're Trembuckers, they're designed for the 2.070" or 52.6mm spacing. All Parallel Axis bridge pickups are Trembuckers. But not all Trembuckers are Parallel Axis pickups.