The 'Stielhandgranate' - which is German for 'handle hand grenade' - was the standard issue hand grenade of the German army from 1915 until the end of WW2. It's extremely familiar to modern eyes, and resembles a potato masher
, a nickname by which it is more familiar.
The grenade was of modular design and consisted of a wooden handle screwed into a cylindrical container of explosive. Operation was similar to a party popper; the end of the wooden handle was unscrewed to reveal a short piece of string which, when pulled, acted as a ripcord, setting off a fuse which ranged from five to seven seconds for infantrymen, down to two seconds for stormtroopers (it's a common misconception that all German grenades were impact fused; some were, but most were not).
Whilst allied pineapple grenades relied on their shrapnel effect to maim and kill, German hand grenade design emphasised explosive force. Thus, the German grenades had a lesser lethal range, but were more effective against armoured vehicles and tanks, particularly against the treads of the latter. A further advantage was that, thanks to the handle, the grenade could be thrown over a greater distance. Soldiers were trained to throw overhand and underhand, and it is wonder that Germany did not, after WW2, become a leading cricket nation.
In some variants of the grenade the explosive section could be removed and used as a smaller hand grenade or, with a pressure plate, as an anti-personnel mine. Furthermore, several warheads could be attached to each other to form a more powerful grenade, and 'splitterringe' - rings of metal designed to enhance the fragmentation effect - could be attached. If all this effort and design expertise had been employed in designing efficient desalination plants or safer and more efficient lighter-than-air transport airships, the world would be a better place.
It's worth noting that the stielhandgranate was not the only hand grenade used by the German army during this time; also common was the 'eihandgranate', or 'egg hand grenade', which resembled Allied designs but was smaller and less effective.