A solid iron newel mount is going to be made possible only by using a good epoxy glue. There are For installing iron newels, I have had the most success with a concrete adhesive. There are a number available and you will want to ask some questions before you buy to make sure you are getting what you want. I think some are available premixed and ready to use and others require mixing. I would highly recommend experimenting with it before you actually are ready to use it to set your iron newel. 

That way you will know a little bit about what to expect as far as how fast it dries and how hard it actually gets.mounting kits available, but I have not used any that end up being solid. They all seem to allow movement.  They also come with a  shoe to cover the mounting kit, and the shoe usually won’t cover the mount.

If you do want to use a shoe to cover the hole around the base of the iron newel, then you will probably need to get the mounting kit.

Different iron newels are different sizes at the base, so make sure you get the correct size shoe.   I will tell you how I have mounted these, and these installation tips are regardless of the type of iron newel.

1. Determine where the iron newel is going.
2. If you are in the process of installing your stair system and can still put in blocking where the iron newel(s) will go, then fill those voids with deadwood 2 X material.
3. You are going to want the iron newel to pass below the floor level at least 3 to 4 inches. Therefore the need for blocking.
4. Determine the size drill bit needed to drill the hole for the newel.  By measuring corner to corner on the newel, you should get a pretty accurate bit size. The hole you drill should be snug to the iron newel. I recommend drilling test holes using different size drill bits into scrap material.
5. Drill the hole for the iron newel. The size bit that this hole requires will make it a little difficult to drill a nice straight hole, so take your time when drilling so the bit doesn’t wander. Stop occasionally to measure the depth of the hole from the floor to the bottom of the hole, until it is the depth you want.  I like to drill the hole at least 3″ deep.
6.  That measurement needs to be added to the overall height that the iron newel needs to be. Measure from the top of the iron  newel where the handrail will set, not the top of the pin, but from the bottom of the handrail, and mark the iron newel to be cut. Where the cut is made is what will be setting on the bottom of the hole you just drilled.
7. Cut the iron newel with a metal cutting bandsaw.
8. Put some epoxy in the hole.  Put the shoe on top of the hole, and tap the iron newel back into the hole inside the shoe.
9. Lift up shoe, and shim around the edges of the iron newel to make it plumb.