Screw Type for Spreader Flag Halyard

My plan is to install a new pad eye for a flag halyard on the lower spreader. The spreader is an Isomat aluminum spreader with a minimum specified wall thickness of 2mm. According to the cross-section diagram the thickness at the middle of the spreader foil MAY be thicker as the diagram shows a thickened area in that location. Accordingly, the thickness then MAY be in the range of 4mm to 6mm (by eyeball).

See url for cross section drawing: http://www.rigrite.com/Spars/Isomat_..._spreader.html

1. Does anyone have experience with the Isomat spreaders to know if the center of the section has a thicker wall thickness than the minimum specified?

2. What would be the best screw type to attach a relatively small padeye: Sheetmetal or Machine? I have no problem drilling and taping for a machine screw and I'd use an antisieze compound in any event.

Any other input would be appreciated. Thanks.