Type 99 (A) 1939

The Type99 "A" can be seen on the 4 photos below.
The grenade functions with the same percussion fuze as the older types.

Total length :
Body length :
Diameter :
Weight :

I got some additional comment about the small brass collar that can be seen on the fuzes' base.
John gave me this explanation :
The collar found on the Japanese T99 grenade serves two purposes. One is that it protects the small delicate screw that retains the brass top cap. The second reason and most important is that it's a flash hider. When the fuze is activated by the primer a flash comes out of the vent hole in the fuze body giving away ones position especially at night. This was an important addition over earlier Japanese grenades whose flash was quit visible.

Type 99 (B)

Text and picture copied from "Japanese Infantry Weapons" cincpac cincpoa Bulletin 55-45, 15 March 1945 :

The Japanese have designed a lightweight, offensive handgrenade; the Type 99 (B).
Unlike the Type 99 (A) it is fitted with a friction igniter and cannot be fired from a grenade discharger. The grenade consists of a smooth cast-iron, cylindricalcasing; a bursting charge of picric acid pressed with a central recess for the powder train and booster; and a fuze.

To use the grenade, remove cover, place ring attached to pull cord over a finger. The ring and pull cord are left on the hand after the grenade is thrown. The grenade may be used as a booby trap by arranging the pull cord as a trip wire, or as a landmine by attaching a long cord and detonating behind cover.