In the USA you will find the Robertson screw hardware and associated drivers referred to as Scrulox.
There are a few sizes, but probably about 80% of the Robertson / Scrulox heads are the #2 size. Robertson drivers are colour coded, the #2 driver will be red coloured.
The next most common is the #3, which if a Robertson driver is used, will be coloured Black.
A set of Nos 1 through 3 is fairly common (Green, Red, Black) and is the recommended set to own; a set of 6 covers all possible sizes, but to be honest the 00, 0, and 4 are extremely rare. Personally, I cannot even recall ever using them.
Trivia:
Robertson patented his screw head in 1908 (Canada) and 1909 (USA, elsewhere) and licensed it to a UK firm, who then proceeded to defraud him by a legal manoeuvre involving a contrived bankruptcy to negate the need for a license.
As such, he refused to license the head to anyone else and that gave the Phillips licensees the traction they needed to become the more widespread type in the USA.
Henry Ford found the system to speed up production and reduce cost, but his attempts to license could not overcome Robertson's stubborn refusal, so that the result was they were used on all Ford vehicles manufactured in Canada but not on any made in the USA.
Almost every screw sold in Canada is a Robertson type, with a hybrid (Robertson, Phillips) also quite common for items manufactured for both domestic and export sales.
