Any unframed board less than 5mm in thickness usually requires a rivet instead of a screw to attached a D-ring as there isn't enough thickness in the material to house a substantial thread.
When possible, using a rivet is a good solution. For a 4mm board (example) the rivet should be at least 9mm long x 2.5-3mm in diameter with the addition of a thin washer on the back of the board to suit the rivet which will sandwich the D-ring between the board and the said washer.
When doing this to acrylic it is strongly recommended that the hole to be drilled in the acrylic slightly larger than the rivet's shaft to allow for slight expansion/contraction in the acrylic and therefore prevent any cracking, also don't drill to close to the edge/corner.
If it is not possible to use a rivet; maybe you don't want anything visible from the front of the panel then laminating the thin board to a backing that has the D-rings attached is another option.
If neither of these solutions work then you need to consider the use of our Acrylic panel holders which can be found on our Accessories page. They are made of Aluminium and will fit boards from 3mm to 6mm in thickness gripping the panel from the sides.
By Luke Norman