The EFT Single is best used for small bull bugles and cow/calf talk. 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 Single is best used for small bull bugles and cow/calf talk. 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!