"Buckeye" couplers have been used on passenger trains in the UK since the 1930s, AFAIK, although for freight traffic they're a more modern phenomenon, mostly post-privatisation. BUT - are these 'buckeyes' the same? I've seen some suggestions that the passenger buckeyes are a lighter/weaker type, while the freight "Buckeyes" are identical to the standard North American "AAR" coupler?