fantomfan57
Garry,
Like Edgar (human) said, could be anything ranging from the 516 up to the Dual Sanitronic 50.
If it has the single-speed safety switch (one button, 134356) then it's a 516 to Sanitronic VII. If two buttons (134365), then Dual Sanitronic 50.
Models 516, 517 and 518, when you remove the motor shell housing, will have a different motor housing casting than models 519 and later.
~Ben