Also known as "Architrave screws" these have a special small diameter head designed to bury into the timber allowing the head to be covered with filler. Basically they are a #7 gauge screw with a #4 gauge head and use a #1 driver bit.
They are ideal for fitting detailed architrave’s as they avoid the risk of damaging the contours. The screw is driven in so the head is just below the surface and a small dob of filler is wiped into the hole making it almost invisible. With the small diameter head care needs to be taken when driving as it can split under high torque.
Origin of the Robertson square drive screws
The "Robertson" screws were invented in Canada by Peter Robertson in 1908. Due to patent restrictions they stayed in Canada for many years and became the standard screw in that country. They are now spreading rapidly through the US and other countries. It is a far superior system and we are sure you will agree “once you use them you don't want to use anything else”.
Not only is the drive system better than the conventional drives, the actual quality of the screws is superb. The screws are extremely strong and the square drive means the driver doesn't jump out and the screw does not break under heavy load.