These items are made using resin printing, guaranteeing a perfect finish and a 4.3mm internal orifice. This orifice can fit a 4mm machined screw or wood screw, but you need to provide the screws yourself. It is best to use a slotted screw, but most affordable screws are made from brass and would require painting. I recommend using black countersunk hex head screws instead. This option ensures that the paint won't chip off when you tighten or loosen the screws. You can choose between the two available options:
 
The Unpainted Version
 
The Painted Version
 
The painted version comes in RAL7011 (Matt Grey). 
Price is PER UNIT (QTY1). Generally, you need four units per panel.