Both these two grenade look the same on the outside, the difference is on the inside and they differ in weight.
The "OO" is an Offensive grenade, the "OD" is a Defensive grenade with a fragmentation liner on the inside of the body.
Both were filled with HEXAL.

Length: 115mm , diameter: 60mm.
Weight and filling: OO : 312gram , OD : 652gram

They both have a spring-powered clockwork fuze for impact and self-destruction.