After a little research, it looks like its a Luftwaffe bomb fuse. I think the clockwork is missing from inside it...almost looks like its actually been used.
Zt Z (89) B
Zt Z = Zeitzünder = time delay (Mechanical)
(89) = The "9" in the circle 89 denotes a Aerial Burst fuze
B = fuse version
The Zt Z (89) Fuze at its variants:
The original Zt Z (89) fuze was only about 55 mm long as apposed to the more normal 110mm fuzes.and came in three types
The contents of this fuze is a clockwork mechanism , similar to the long delay (17) fuze it fact it was manufactured by the famous Jurgens clock factory.this clock ran for a maximum of 80 seconds , the delay being varied by pushing down the centre plate and turning it , using a special setting tool. The case construction was aluminum
The (89) B version had a delay from 1 to 80 seconds and was the normal full length fuze of 110 mm and was constructed of rolled steel, next came the (89) C version this had a minimum delay of 2 seconds and a maximum of 160 seconds .
Markings on the B and C charging plate reads NUR FUR HAND EINSTELLUNG which translates as ONLY FOR HAND SETTING.
Pics I found of the fuse and tool used to set time delay: