Steel cap screws come in a few different head designs and finishes. They are an ideal screw for creating a very secure fit between two other materials. More importantly, they can effectively become almost invisible if you know which type and finish of cap screw to use. Here is how to make cap screws "disappear" but still function as intended.
Head into Machinery and Materials
Choose a Phillips head cap screw, an Allen wrench cap screw, or a flat head socket screw. All three of these can be screwed into openings between two flat panels of metal, wood, etc., and disappear when screwed in far enough. For example, the flat head socket screw's unique head shape becomes flush with the surface. If you were not looking for the top part of the screw where the screwdriver goes, you would not be able to see or feel the screw. If you fill in the head or cover the screw with a little cold solder, you would never see the screw again (at least, not until you scrape/break the cold solder off).
Cap screws, regardless of cap head style, come in a variety of finishes. If you want your screws to blend in and almost disappear, buy the ones that most closely resemble the finish of the materials, machinery, or object into which they will be screwed. For example, If you have a slate black metal sheet and you want to fasten it to a wood surface, you can pre-drill the hole for the black cap head screw, and then drive the black metal finish cap screw through the pre-drilled hole. From twenty feet away, you may not be able to see the screws when they are the same color as the material around them. You would have to get up close to see them and actually be looking for the screws to spot them.
Hooking, Fastening, and Hiding
When you really do not want your cap screws to show, use another sheet of metal that has all of its edges folded over and pre-drilled to match the holes in another surface. You will drive the screws through the holes on the folded edges of the sheet metal into the holes of the other material or the machinery. You are creating a sort of flat pocket around the attached machinery or material. When screwed in correctly, you cannot see nor find the screws at all.
For more information, contact companies like Jackson Bolt & Screw, Inc.