Above is the mystery FRT-3 (left) and Double Eagle FRT-5 (right). Notice they both have a slanted brass block, although the FRT-3’s version is thicker.
Although the mystery FRT-3 maintains very high quality equaling the production FRT3’s, the FRT-4 and FRT-5 copy do not seem to match the quality of their official Floyd counterpart during the time.
So who made them? We will never know, but as mentioned earlier, the Double Eagle FRT-4 and 5 copies are rumored to have been made by Gotoh or Double Eagle, but nothing is for sure. The Mystery FRT3 seems to be an official Floyd prototype but deviates with the other prototypes with its sustain block and saddles.
If you have any information on these Pre-Schaller mystery tremolos, please contact me.