Humbuckers and Trembuckers are very similar to each other, and most humbucker models also come in Trembucker versions. The Trembucker-spaced JB, for example, is a TB-4 and the humbucker-spaced version in an SH-4. The only difference is the wider spacing of the pole pieces on the Trembucker versions. This spacing issue only applies to the bridge position pickup, which is why Trembuckers are recommended for the bridge position. Trembuckers are designed for wider string most commonly associated with Floyd Rose or vintage vibrato bridges (often called Tremolos) with a string spacing of 2.070" or 52.6mm, measured center of high string to center of low string over the bridge pickup. Humbuckers are designed for bridges with traditional Gibson humbucker string spacing of 1.930" or 49mm, measured center of high string to center of low string over the bridge pickup. Humbucker spaced pickups work in both bridge and neck positions, even with a Trembucker-spaced bridge pickup. A quick and easy way to tell which you need is to measure from the middle of the high string to the middle of the low string, directly over the pickup. If the distance is greater than two inches or 50mm, go for a Trembucker. If it's less than two inches or 50mm, go for a humbucker.