They were known as a potato masher !
Under the cap, at the bottom of the handle, there should a porcelain bead attached to a length of string.
Unlike the majority of hand grenade designs, the Stielhandgranate design was ignited by friction. Inside the hollow wooden handle, a steel rod was attached to that string. After the string was pulled, a shower of sparks lit a fuse that burned for approximately 4.5 seconds before exploding.
Have fun ! :~)