VEVOR Handrails for Outdoor Steps, Fit 3-5 Steps Outdoor Stair Railing, Wrought Iron Handrail, Flexible Front Porch Hand Rail, Black Transitional Hand railings for Concrete Steps or Wooden Stairs

The base has the seating plate with the holes to bolt to the surface where you have placed the railing…. The square cover drops down over the seating plate to “finish” the look of the railing and protect the bolts from weather…. Hopefully this helps

they are for fitting the 2 trim plats together. One side has holes and the other has tabs.

Not sure I had any holes in the base trim

You'll need to drill holes into the concrete steps to bolt the posts to. Four holes per post (bottom flange).

Location of drilling holes to install the expansion bolts to hold the railing in place. Comes with a cover cap. You need a cement drill bit

Not sure I understand the question. The holes in the base plate are where the bolts go to secure the handrail to the steps.

I have handrails with 2 vertical posts and only one horizontal (ish) top rail and all 3 are aluminum. Even the welded bottom flange (with cover) is aluminum.

All the main part are aluminum.. I just installed and it’s very sturdy

The whole this is aluminum.

It is all aluminum.

I believe that all pieces are aluminum. It appears sturdy. We've had ours for two years and it still looks beautiful. I did use rust-proof black paint on the heads of the bolts and screws, just in case.

it's all iron I believe.

All 4 parts are aluminum