The Barless Top-Lok is a type of locking nut designed by Ibanez and installed on some Ibanez guitars.
A locking nut is generally used along with some sort of tremolo bridge to maintain tune when the tremolo is used. It locks the strings against the nut which improves the tuning stability when using the vibrato bar. The drawback of the locking nut is that the nut must be loosened with an allen wrench if the player needs to tune beyond the range of the fine-tuners on the bridge.
The design of the Barless Top-Lok eliminates the retainer bar which is common to many locking nut designs. This design uses three (or four on seven-string models) allen screws which compress three pressure pad saddles securing the strings against the nut.