If I'm honest, I rarely bother with the springs that accompany some 3-link couplings. I'd much prefer to fit sprung buffers, and I can't say that I've ever had a problem arising from the lack of sprung coupling hooks.

This all makes the fitting of coupling hooks like Smiths to RTR wagons much more straightforward. My methods, when described on here from time to time over the last few years, sometimes raise eyebrows, but they do work and I've rarely had any subsequent problems.

I file the shank of the hook down, sometimes reducing it's width by 50%. I also shorten it by 30 - 40%, and file the end to a sharp point. I then assemble the screw, instanter or 3-link assembly on the hook.

I then remove the plastic hook from the Bachmann or Hornby wagon, and remove any excess plastic carefully, with a very sharp scalpel. A 0.5mm hole is then drilled into the centre of the hook aperture in the buffer beam (the original hook rarely comes out whole).

The next bit works best if you've got a gas hob in the kitchen...

Holding the coupling assembly and hook in thin pliers, the sharp end of the shank is heated up in the flame and quickly but carefully inserted into the 0.5mm hole and gently pressed home, until the visible part of the hook is all that's left (plus the links, of course).

No glue or dismantling of RTR wagons required (although I usually take them apart to put a bit more weight in, if it's for P4, don't usually bother if it's for OO).

I prefer Smiths because their somewhat overscale hooks work best for me, especially when being observed under exhibition conditions!

Hope this helps.