Great job on the mallet. I am curious as to why a two piece when the blank looks large enough to do it all?

 

@forty_caliber brass will turn with regular hss or carbide.

There is no need to pin it due to the glue and the size of the tenon but you certainly could. Brass turns very nicely with HSS or carbide chisels. I incorporate brass in my turnings without any difficulties. 
Paul

Here is a better picture. 
Paul

27 minutes ago, Masonsailor said:

Here is a better picture. 
Paul

Beautiful work.  What method did you use to incorporate the brass.  I'm guessing a plug cutter to relieve the wood for a piece of brass pipe.

 

.40 

I drilled holes on the segmented ring to insert small sections of brass pipe. Before glueing them in I took small pieces of the Brazilian walnut and just pounded them in with a little epoxy. The pipe sheared off the wood as I drove it in. 
Paul