Square Drive vs. Phillips-Head Screws
What’s the advantage to square-drive
screws over Phillips-head screws?
The primary advantage to square-drive screws is
they are much less prone to “cam-out.” Cam-out
refers to the slipping of the bit in the screw head
as the screw is driven.
The square-head screw was invented by
P. I. Robertson, a Canadian, in 1908. It offered a big
advantage over the slotted screw head because it was
self-centering and not prone to slipping when driven.
But, an early attempt to market these screws in the
United States failed. This left the Robert-son screw
confined to the Canadian market.
The Phillips-head screw was initially developed in the
1930s for industrial use. It offered the same self-centering
advantage as the square drive but was designed to
cam out. Cam-out was considered an advantage in the
industrial assembly line, preventing screws from being
overtightened and giving a little cushion to the furious power drivers of the day. But the advantage for industry
was the bane of woodworkers. Cam-out for them
meant marred finishes and scarred wood.
Eventually, the Robertson-head or square-drive
screw migrated across the border and, by the 1970s,
was making strong inroads in the furniture and
A new hybrid screw-head design is a square-drive
screw that, in a pinch, allows you to use a Phillips driver.