Robertson Drive Bit: #2, 4 inches
Although the terms "square drive" and "Robertson drive" are often treated as the same, there is a big difference - Robertson drives and Robertson screws have a slight taper to the square recess and a square drive and screw does not.
Robertson drives were invented by Canadian Peter Robertson around 1906 and are very popular and common in Canada, but not so much elsewhere.
The advantage of using a Robertson drive with a Robertson screw is that the screw will "cling" to the driver, allowing one handed driving and virtually eliminating slippage common with drives such as Phillips drives.
These #2 Robertson drive bits fit our Rob Cosman screws with their duo Quadrex heads perfectly. While a #2 square drive will also work, it doesn't fit the screw head perfectly like a Robertson and will not give you the "cling" feature.
We highly recommend you use Robertson Drives with our Rob Cosman screws.