That is not only a Garrett BFO, since it is single winding coil, I would say it is for the Garrett HUNTER BFO model, which dates it up into early 1970s time period. Now Carl (NC) also said Garrett BFO, and you have it now identified accurately. The Garrett Master Hunter BFO series had a smaller coil inside the larger coil and the Master Hunter could switch between one or the other of the coils.
Melbeta