If I understand your reasoning right then your "plugs" are intended to be slid in and out when rigging or derigging the part/boat. First of all, this assumes that the connections can only had when such a fitting it used, this is not the case. There are non-plug-sliding alternatives. I'm using one of those. My setup uses at this time only eye/bolt and eye-bolt/fork connections. The latter being rigged/derigged by clevis pins.

But to answer your question directly. Bajonet fittings come very close to what you are describing. You can always route a groove in the plug with a straight angle in it. The bulb of the rivet then runs through this track and by rotating the plug you secure it axially. Securing the rotation of the plug is not needed in all instances but when it is then there are quite a few alternatives as well.

I'm still waiting for the Hawaian clamp description. But it it is what I think it is then that is also a way to secure the brace to the mast, this time without any clevis pins or bolts what so ever.

Of course one can always use clevis pins to secure part that slid into a tube and need to be taken out often. As the rods in the F12 design are most heavily loaded by compression the clevis pins don't have to take the real loadings as a simple rim on the end of the plugs resting on the tube endings will take care of that. Again, that is what my design is now using. That is another reason why the push rod setup is advantagious. Basically the way things are now the plug is most pushed deeper into the rod. Securing this has endless alternative. An additional brace running from the sides of the push rods and around the front of the mast will then be there to prevent the mast from being pushed out to the front on downwind legs. This brace can even be a simple lashing. I say "can" here as I personally prefer a stiffer method of fixation, but the point made is simple enough. You can actually use rimmed plugs that just slide into the push rods and have a single brace (=lashing) fixate the whole setup in one go. Easy, quick and inexpensive to make if we repeat setups like this often enough then we may well get very close to the stated design goals, the 100 hour building setup included.

I'm sorry I can't provide you with drawings of these setups as that will take to much of the spare time I can spend on the F12 project. However, I think these verbal describtions will suffice.

Wouter