This tool shall be made(turned) from one piece to ensure the pilot hole is exactly 90 degrees to the jig base. The purpose of the tool is to ensure the drill bit is kept "SQUARE and centered" on the spar rivet as you drill .
The counterbored hole will be as near as possible the size of the mushroom shop head AD5 (approx 8mm.)AD6 (approx 10mm)
A 3mm Transfer Punch will be inserted through hole and used to accurately pick up the small dimple in the centre of the AD rivet prior to finally clamping of the jig in position.
You then drill through approx 3/4 of rivet using a 3mm drill ,this is around 1.1mm undersized in relation to the outside diameter of the AD5 rivet this will ensure that the drill does NOT damage the hole sides .
By drilling around 3/4 through the rivet this will also relieve the expansion pressure of the rivet core and leave us with a "blind hole "thus allowing the rivet to be tapped out using a 3mm parallel punch.