The various parts of the combination square set can be removed from and put back on the rule through use of a screw or nut, which secures them to the rule.
This is useful for when you need to use one specific accessory.
This can be done because the rule is grooved on one side, allowing the accessories to slide on and off.
Sometimes the user may find that the rule of the combination square set may have marks on both sides.
As a result, the accompanying heads may come with locking nuts which can be rotated 180 degrees, to allow the rule to be turned around.
Inside the various heads is the little device which secures the head to the rule.
When the locking nut is turned around…
…the device is also turned around.
This means that the rule can be used with the groove on “either side”.
