I have in my collection two, Type 97 grenades, small compared to the British mills bomb and the American MK2 pineapple grenade. I noticed the other day that the diameters we slightly different to each other. One measured at 46.8 mm the other at 48.5. In my newly acquired Japanese ordnance manual the diameter measures at 49.8 from the drawings. Having a chat to someone the other day they mentioned that there were different factories that made these grenades as well as overseas factories, wondering if this was the reason why and if there was any truth in it. Any grenade collectors out there that have noticed the small diameter difference.