Exactly. For the uninitiated this racquet is a bit hard to explain. In the 60's, Tretorn had this idea that stringing was cumbersome and/or too expensive to do regularly, so they released a racquet where you could swap out the entire hitting surface by loosening a few screws.
Strings gone dead or you broke one and it's your only racquet? Easy! Go to your bag, get your extra head, unmount the old one, in with the new, and voila! Back on the court in about 3-4 minutes!
The racquets I've been told are rare as hen's teeth even though I've found 4 or 5 of them before (Tretorn had their factory in this city before) and spare heads I believe are even rarer. Especially since both of them are in the original bag and one of them literally have never seen a tennis ball. I'm also guessing these were made quite late because they had the newer Tretorn stencil as opposed to the other one.
So as to not bore you any further, here's a 6 year old picture I'm borrowing from myself so that you get the general idea of it (And I realize that I had literally just turned 16 when I posted about this the first time...)
I don't have a racquet frame for them right now, but I can conclude from the last time I had one that it's an apocalyptically awful piece of tennis equipment. The flex combined with the disconnected feel of the stringbed... Just no.