It isn't exactly a standard hammer? [Actually since this is a mirror conversation, Lenka will notice that John's moving and turning his mirror shard to show off a hammer.] But yes, it is a hammer.

[Even if the view isn't on himself right now it's obvious he finds amusement in his own plight given how he sounds.] As far as I can tell it's being able to combine any two items together. I have not found a size or capability limit yet, but it definitely can't be more than two. It's both awesome and kind of stupid.