The drive size determines the torque range and the access, and using the wrong size is either ineffective or breaks the tool.
Drive size sets the capability. 1/4 in drive is for small fasteners and confined spaces, up to roughly 15 ft-lb. 3/8 in drive is the general-purpose size, covering most automotive and equipment work up to around 80 ft-lb. 1/2 in drive handles heavier work to about 250 ft-lb. 3/4 in and 1 in drive are for heavy equipment and structural bolts.
Socket type follows the fastener. Six-point sockets grip the flats and are less likely to round a fastener; twelve-point sockets engage at more angles and are useful in restricted access, but they bear on the corners and can round a tight fastener. Impact sockets are made from a tougher steel and must be used with impact tools — chrome sockets shatter under impact.
Extensions, universals, adapters and breaker bars extend reach and leverage. Long extensions reduce the usable torque and increase the tendency to twist off; wobble extensions and universals allow access at an angle. Torque wrenches are the tool for anything with a specified torque, and their range must bracket the value being applied.
