I could very well be an 1913 german kugel handgrenade. Later models had a different, easier to machine fragmentation pattern. There 5 or 8 sec delay fuse activated sec by a pin on top you had to pull out. They were quite heavy and were replaced by the famous potatomasher grenade.

Hi. Though I realise this has only been up six hours so there hasn't been much of a chance for people to answer, you may also have luck on /r/whatisthisthing.