It is a ¼”x20 standard thread. This is compatible with all AbleNet mounting systems.
The Mounting plate was designed to universally fit a variety AbleNet switches and devices. Depending on your application there will be parts in the box that are unused.
The locking knob should be screwed to the bolt of the Universal Mounting plate prior to inserting it into the mounting arm. The orientation of this knob should be where the flat end is towards the mounting arm. This allows you to secure the knob to the mounting arm, which locks the mounting plate into a fixed position when secured to the mounting arm.