Some of the most commonly used hex bit sizes for FIRST robotics:

• 1.5mm for REV Robotics Shaft Collar set screws

• 2.0mm

• 2.5mm for goBILDA low profile M4 screws

• 3.0mm for goBILDA M4 screws

• 4.0mm

The ends are magnetic to help avoid dropping screws into the center of your robot! The shafts are long (150mm / 6 inches) and thin enough to fit through the holes in goBILDA channel.