I don't know what or how to identify this switch.
Its dimensions are:
29.5mm by 25 by 21.5 tall. It has a lug for a screw on the side you can't see it is actuated by a pin on a separate housing
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Stupidly I hadn't looked at another image I had which clearly stated 'XE2SP' which promptly gave me the manufacturer and terminology.
SCHNEIDER ELECTRIC / TELEMECANIQUE - XE2SP2151 - CONTACT BLOCK
Maybe an Eaton or Cutler-Hammer safety switch, though it's really difficult to guess from the limited information.
Can somebody let me know what form factor this is
In EE (and physics apparently) form factor is defined as: -
The ratio of the RMS value to the absolute mean of a sinusoidal wave (especially to that of an alternating current)
Taken from here
If you are wanting to know the form factor as defined by EE guys then it doesn't apply to a switch - it's to do with electrical signals.