>Is there any difference between t120 us handlebars & t140 us ones as I seem to have a liking for the t120 ones

As you already seem to know they are not the same shape then I'm not sure what else it is you think might be different?
The T120 was made from 1959 to 1974 during which time there were several variations of "US" handlebar (and not all years of T140 US handlebars are exactly the same) so perhaps you could narrow it down a bit regarding the T120 model year?


>+ are they the same dia tubing?

Triumph handlebars were 7/8" (22.23mm) diameter from 1963, prior to that they were 1 inch.
Note that handlebars available nowadays can often be made of 22mm tubing and although not much smaller in diameter it can sometimes be enough to make the difference between throttle housings and switch assemblies that clamp tightly to the bars and ones that don't!