The Type10 defensive grenade was the first mulitfunctional grenade used by Japan.
It could be delivered to the ennemy in three different ways.
By hand, by rifle or as a mortar grenade.

Details on the fuze
The base held a propelling charge when used as a mortar.

Photos thanks to Dr. Ruby

Shown right is a Type10 Training grenade. It has a solid base with small drilled holes of only 3mm deep.
The top could hold a normal fuze as in has standard threads.

Length: 102mm, Diameter: 53mm. Weight: 625gram

Here on the right is a similar practice grenade, with a minor difference in detail.
The top has a small upstanding collar, and has normal threads as well.
I don't know if this is earlier or later then the body shown above.