I am looking for a hair spring replacement for a Zodiac SST3600.  The movement diagram shows the part number to be 734.  Is there a suitable replacement since this is a high beat movement?

In all the years of buying thousands of parts for Zodiac I have never encountered seperate sealed factory hairpsrings for any of the models.  From the factory literature, Part 734 is supposed to be "Flat Hairspring, Regulated".  However, it would be much better to find a balance complete even if you had to buy a parts movement.  The balances in the Zodiac calibers 70 - 88D are pretty durable and rarely have broken staffs or damaged hairpsrings except for repair error, so a decent parts movement will often have a usable balance complete.

Even if you are able to obtain a new hairspring then you need to "pair" it with concrete balance wheel. Which is complicated operation (vibrating balance) and requires special equipment. Usually it is done on watch factory. So, indeed, balance complete from a right donor is your viable option.
https://www.youtube.com/watch?v=GSIOZCwlimQ

Quote from: YuriyV on February 11, 2025, 03:29:57 PMEven if you are able to obtain a new hairspring then you need to "pair" it with concrete balance wheel. Which is complicated operation (vibrating balance) and requires special equipment. Usually it is done on watch factory. So, indeed, balance complete from a right donor is your viable option.
https://www.youtube.com/watch?v=GSIOZCwlimQ

My thought as well.  I have not vibrated a 36000bph balance, not sure I am in a hurry to either.  Especially considering the availability of balance completes from donor movements in the used parts market.