Hi dear,
Here you can see my construction of a tack bra.
http://www.imagebam.com/image/83fead459634665
Tack bra inside with penny washer: 15mm diameter, 1,2mm thickness. Pressing the tack bra tissue between the nail head and the penny washer makes the nail is always perpendicular to the bra tissue. No glue at all.
Outside view of the tack bra with nails: 3,1mm diameter, 15mm length. Nail head diameter: 9mm
http://www.imagebam.com/image/7223e6459634667