How to determine your alternator type
 

I recently needed to change the pulley half, shims, alternator nut and cap on my early 911.

When purchasing the alternator nut and cap I was confronted with a dilemma, did I have the Bosch alternator or Marchal alternator? The sizes for these nuts are different. I couldnt find any help so I thought I would post the method I used to determine the difference in the hope that it may help some one some day.

The Marchal alternator has an M16 sized thread and therefore the socket size to fit it is 24mm.

The Bosch alternator has a M14 sized thread and therefore the socket size to fit it is 22mm.

I hope this helps.

Thanks for the information.