This is not a tool I think I've ever used but it is definitely one of my favourites. My grandfather was in the garage trade for a time between the wars and this was one from a box of spanners I rescued when we were clearing his home garage. Wiki tells me that the Darracq name was dropped from the then S-T-D combine in 1922 so presumably this predates that. It always makes me think, just how impressive was the car (or truck?) that this originally belonged to.