Regards the recent posts about the original Duffus trap being better than the later incarnations I gave my traps a good coat of looking at this morning. I've got a second generation Duffus, marked J. Duffus & Son, but not the Patent. It needed a bit of fettling as you would expect for a trap around 40 - 50 years old, but really it was only the wires that needed rubbing down and the usual mods made to the triggers as it was unadulterated when my mate gave it to me.
My mate who gave me this trap and some others including a similar, but unbranded Duffus type trap from the same era only did a bit of moling so they haven't had much work. Both are still working and could be used.
This Duffus trap is significantly different to the modern Flatpacks I've got. The most noticeable thing is that it is a lot narrower and has a steeper arch than the Flatpacks and other cheaper traps I own. Across the tape measure the Duffus is 60mm wide whereas the original Flatpack Ultimate Stainless trap is 70mm and the more recent version of this is a whopping 74mm across the arch. When I got these later traps I phone the company and asked if they had sent the right traps as they are different in size and finish to the ones I'd previously bought, but they denied any knowledge. The cheaper galvanised Flatpack that all you poor folk (and me in future) is 70mm across.
The internal measurements, i.e. the trapping wires are much the same, both around 55mm, the Duffus has a slightly wider profile towards the bottom. But for me, the extra width of the Flatpack means that I have to make the hole bigger above the tunnel to accommodate the trap body. In turf I usually grip the roots with my fingers and squeeze them back. In clay soil it means slicing it slightly wider at the top of the mole's tunnel or the trap will pare earth down inside the tunnel and the trap.
Now, I don't share Matt's view that the old Duffus is a better trap than the quality modern ones. The Duffus has a square bottom that to me is undesirable and the loop of the retaining wire isn't manufactured perfectly round and so is a pig to set. Incidentally this wire is opposite handed to modern traps and feels awkward when manoeuvring it under the trigger loop. The S/S Flatpacks I got about three years ago knock it into a cocked hat in my opinion. The wires are slightly wider, they run through the slots smoother and the trigger loops are more substantial. The more recent S/S Flatpacks however, are a pain because of the unnecessary width of the body.
Now everybody has a vice. Mine is in the basement bolted to a work bench and that proved to be the answer. Take one Flatpack Ultimate Stainless Steel Trap, place it in the vice, squidge it from 70mm to 60mm, remove from vice and you have the ultimate tunnel trap bar none in my humble opinion.