horizontally* (I check that they fall under their own weight when the vehicle is held on its side), but not vertically. The brass rivet needs to be fully 'home'. The rivets can be tightened by pressing a suitable nail into the hole in the top of the rivet. (rest the bottom (head) of the rivet on a solid surface (vice for instance) and press the nail into the top to fix/tighten the rivet. (In the absence of a press a gentle tap with a light hammer might work.) Conversely a thin steel rod will allow the rivet to be pushed out (and reused in contrary to drilling it out) to remove couplings for reuse, derusting** etc.. *The couplings will still function if one of them is stiff/seized, but not both. Stiffness is another source of undesired uncoupling, as it won't give the flexibility needed to go around curves (especially the Dublo tramway type). **I use a brass brush in a mini drill for this. In mild cases the rust goes, but not the finish. Other types of couplings seem less susceptible. Kadees and X2fs* seem to stay locked and the vertical acting coupling are held coupled by their weight, though even here 'bounce' will provoke unwanted uncoupling. Here the same rules of free movement and standard height apply. * These have a section of the uncoupling dropper which helps to prevent the hooks getting out of alignment. They are held in engagement by a spring (this is often too strong