Every stanchion base is the same procedure but the stand alone stanchion is different there after.

3.18mm bore brass tube set for soldering. My centre height from deck is 35mm at the centre line of the foot

Trim off the other side and repeat soldering.

Then grind off both sides near to their final length.

drill from both sides 1mm

Follow both sides with one of these at 3.18mm also

Only as deep as the solder

2mm bit NO BIGGER from both sides also, smaller if you choose.

to be continued ......