This is the MH1620, more commonly known as 1420. It's 14mm across the flats, 16 on the diameter and 20mm long. These are left over from our final run of LoRiders and we won't have any more, but it's better off going to someone who needs it than sitting here as a memento. They were a very popular motor and a useful size, with common uses being in an upright plane, located in a fireboxin tender goods engines like LNER Q6s etc.