This is the 1st trumpet model Olds produced, up until this point they made trombones only. This trumpet simply called "The Olds" was available in 3 bore sizes; M (medium), LM (large medium), and LLM (large large medium). This one is LLM and measures .455 or so. I had also gotten a medium bore NY Bach when this came my way and they played very similary. Great old Olds trumpet.