The EFT Double is best used for mature bull bugles and grunts. EFT Extended Frame Technology was created by extending the frame upward and inward creating a simple yet effective system for securing the call in place for a perfect fit every time. A great fit equals a great sound, hear the EFT difference!The EFT Double is best used for mature bull bugles and grunts. EFT Extended Frame Technology was created by extending the frame upward and inward creating a simple yet effective system for securing the call in place for a perfect fit every time. A great fit equals a great sound, hear the EFT difference!