Bourke Installation
To install Bourke spikes on your helmet without having Bourkes
(preferred) borrow a set of Bourkes from a coworker (in case you decide you want Bourkes in the future they will be lined up correctly)
Position the shield on your helmet so that the inner edge of the brass frame is about 1/2 to 3/4 of an inch from the outer edge of the helmet dome.
Mark the position of each of the two screw holes in the shield by making a dot or "x" on the brim of your hat for each hole before you remove the shield so that you can drill mounting holes.
Drill a hole in each of the two marked spots. (3/16" for 10-32 screws, 11/64" for 8-32 screws)