Old people like me sometimes need a steadying influence as we walk past the head of the stairway at night. Two of these brackets (you need one left hand and one right hand version) support a standard hand rail sufficiently well to run your hand along it as you pass the stairway. It is easy to tip the top toward you to remove. The only modification to the hand rail is to remove 3/8 in. of the lower rib on all 4 corners. Tinkercad creates right and left hand versions quickly with the Mirror tool.

When printing it is a good idea to increase top, bottom and vertical walls to 4 layers minimum. Maybe 50% fill overall.

I think the countersinks are for #10 screw.

TinkerCad file is available here I think?
https://www.tinkercad.com/things/b3rLtzLgh13-hand-rail-support-lt-hand

Use at your own risk.

Print instructions

When printing it is a good idea to increase top, bottom and vertical walls to 4 layers minimum. Maybe 50% fill overall.