Discontinued Mainspring - How to Choose Next Best Size

[RickTock]

How do you decide which mainspring size to go with when the one specified for your movement is discontinued?

For example, I have a movement that calls for a mainspring with the following specs:

• Height: 1.60
• Length: 280
• Strength: .105
• Barrel Diameter: 8.5

Or more simply stated: 1.60 x .105 x 280 x 8.5

It is discontinued, so a couple close ones from Cousins would be:

• 1.60 x .105 x 260 x 8.5 -- shorter by 20 mm but otherwise same -- so less power for sure
• 1.60 x .11 x 270 x 8.5 -- shorter by 10mm but .05 stronger (thicker) -- so maybe same(ish) power but hopefully not too much?

My gut tells me the second one would be closest to the original, but I don't have enough experience to say definitively.

Is there a mathematical formula I could use to base my decision? What would a seasoned watchmaker do?

Thanks!

[fclass308]

I would err on the side of the stronger spring if those are your only 2 choices. I'd bet it will work just fine.

[RichardHarris123]

Only the strength is related to power, not the length.  Shorter spring, less reserve.  You usually don't want more power, so go for the  .105.

[AndyGSi]

So the first question is what's the movement and is it Automatic or Manual.

As @RichardHarris123 said you don't want to go for a stronger spring.

[praezis]

Length is the least relevant size.

Even the difference of reserve will be minimal.
And with 260 your watch will run longer  (2%), as 280 is longer than optimum.
For your barrel strength 10.5 is already on the stronger side.

Frank

[mikepilk]

2 hours ago, RichardHarris123 said:

Only the strength is related to power, not the length.  Shorter spring, less reserve.  You usually don't want more power, so go for the  .105.

I used to think the length only effected reserve, but the length does effect strength, though probably not a lot. Imagine a spring only 25mm long, how strong that would be compared to a much longer one.

The spring is effectively a beam in bending, so the moment of Inertia is (width x thickness³)/12. So the thickness is much more important than the width.

With your spring choices (0.11/0.105)³ is a about 15% increase in strength. 

The lengths are so similar, I wouldn't worry about that

[AndyGSi]

Everyone appears to be overlooking the fact that although the GR4502
has been discontinued there are still genuine ones available.

[mikepilk]

Gleaves have this  https://gleave.london/mainspring-1-60-x-0-105-x-280-x-9-00-manual/

[RickTock]

8 hours ago, AndyGSi said:

So the first question is what's the movement and is it Automatic or Manual.

As @RichardHarris123 said you don't want to go for a stronger spring.

The movement is an AS 1194, manual wind. The relationship between strength and length was really confounding me, but advice in this thread has added some much appreciated clarity.

4 hours ago, mikepilk said:

Gleaves have this  https://gleave.london/mainspring-1-60-x-0-105-x-280-x-9-00-manual/

Thanks, I appreciate that (and the eBay spring @AndyGSi posted). If there was nothing close at Cousins, I would be chasing one of these.

[AndyGSi]

If you just want to use Cousins then I'd go for the GR4501

[RickTock]

7 hours ago, mikepilk said:

With your spring choices (0.11/0.105)³ is a about 15% increase in strength.

A golden nugget of knowledge. Thanks for sharing that!

[mikepilk]

27 minutes ago, RickTock said:

The movement is an AS 1194, manual wind. The relationship between strength and length was really confounding me, but advice in this thread has added some much appreciated clarity.

Thanks, I appreciate that (and the eBay spring @AndyGSi posted). If there was nothing close at Cousins, I would be chasing one of these.

Although I buy nearly all my stuff from Cousins, I recently started using Gleaves.  They had some parts that Cousins had discontinued. It's not so easy to find stuff on their site, but prices are good, and the service has been excellent.

[RickTock]

3 minutes ago, mikepilk said:

Although I buy nearly all my stuff from Cousins, I recently started using Gleaves.  They had some parts that Cousins had discontinued. It's not so easy to find stuff on their site, but prices are good, and the service has been excellent.

Thanks for that. Just had another look at Gleaves site again. Their shipping costs are in line with Cousins also, both of which I consider quite reasonable for shipping to Canada.

[mikepilk]

56 minutes ago, RickTock said:

Thanks for that. Just had another look at Gleaves site again. Their shipping costs are in line with Cousins also, both of which I consider quite reasonable for shipping to Canada.

I didn't realise you were in Canada. Are there no watch part suppliers in Canada? 

There must be suppliers in the US, but you may not want to use them (the way things are going the tariffs could be about 5000% by the time you order ).

There is one supplier I've used many times in the US you could try https://www.daveswatchparts.com/ . A one man operation, very helpful. 

[tomh207]

This place would be worth a look seeing you are in Canada 

https://perrinwatchparts.com

 

Tom

[praezis]

8 hours ago, mikepilk said:

Gleaves have this  https://gleave.london/mainspring-1-60-x-0-105-x-280-x-9-00-manual/

For mounting this spring, you will need a suitable winder, direct pushing into the barrel is not possible (9 > 8.5)!

Frank

[mikepilk]

47 minutes ago, tomh207 said:

This place would be worth a look seeing you are in Canada 

https://perrinwatchparts.com

I had a look there - they had only two types of non auto mainsprings, $78 !

4 minutes ago, praezis said:

For mounting this spring, you will need a suitable winder, direct pushing into the barrel is not possible (9 > 8.5)!

Maybe, have you measured the barrel?

[praezis]

17 hours ago, RickTock said:

• Height: 1.60
• Length: 280
• Strength: .105
• Barrel Diameter: 8.5

[RickTock]

3 hours ago, mikepilk said:

I didn't realise you were in Canada. Are there no watch part suppliers in Canada? 

There must be suppliers in the US, but you may not want to use them (the way things are going the tariffs could be about 5000% by the time you order ).

There is one supplier I've used many times in the US you could try https://www.daveswatchparts.com/ . A one man operation, very helpful. 

Yes there are a few suppliers in Canada. Perrin, Somal and at least one more that has slipped from the front of my memory. And there are several US suppliers closer to home than Cousins.

I try to shop local (i.e., within Canada) but I have found Cousins has the best on-line inventory, and as such I always have a few things in their shopping cart (that I can't find in Canada) awaiting sufficient order size to warrant shipping. I do shop local if I can find enough of what I'm looking for from Canadian suppliers, and it is particularly convenient if I need parts in a hurry. But ordering from a Canadian supplier always means I'll inevitably be paying for shipping on two orders instead of one (one from the Canadian supplier who has some of what I need, and Cousins who has everything else). 

Cousins will ship via Royal Mail which converts to Canada Post once landed in Canada. It is reliable and economical. My small orders zip through with no added tax or duties. Most US suppliers insist on using one of the big courier companies, all of which are prohibitively expensive for cross-border shipments because they charge hefty brokerage fees even on orders worth a few dollars.

And although I could have explained myself better in my original post, I was more interested in understanding the relationships between mainspring parameters than necessarily tracking down exactly the specified mainspring for the movement I'm working on. But this is such a wonderfully helpful forum that I got two for one! Both the coveted knowledge I was seeking, and some great tips on where to buy the mainspring I need.

I really appreciate everyone who jumped in here.

[AndyGSi]

Can you measure the internal of the barrel to see if a 9mm supplied spring would fit
directly as this could be vital information for someone else who comes across this post.

[mikepilk]

4 hours ago, praezis said:

Height: 1.60

Length: 280

Strength: .105

Barrel Diameter: 8.5

I was assuming these numbers are those for the spring spec, and not the measured values 

[RickTock]

5 hours ago, AndyGSi said:

Can you measure the internal of the barrel to see if a 9mm supplied spring would fit
directly as this could be vital information for someone else who comes across this post.

The inside diameter of the barrel from the AS 1194 movement I'm working on is 9.2 mm.

The 8.5mm dimension quoted in my original post is from the GR4502 mainspring dimensions Generale Ressorts specifies for the AS 1194. 

Speculation on my part would be that the Gleaves 1.60 x .105 x 280 x 9 Manual spring kindly noted by @mikepilk would be a perfect fit, and likely differs from the GR4502 by being supplied in a washer with an internal diameter 0.5mm larger.

[JohnR725]

15 hours ago, RickTock said:

The movement is an AS 1194, manual wind.

2 hours ago, RickTock said:

The 8.5mm dimension quoted in my original post is from the GR4502 mainspring dimensions Generale Ressorts specifies for the AS 1194. 

All of us approach the problem differently possibly. I like to have a number for watch which we get much farther into the discussion and I looked up and I get the following information

MS-711K   MAINSPRING 1.60-.10-300 9   GR 4486

Then eBay for instance looks like you can buy five of them. It was the first number that I was looking for as that's the most likely number if I search for on eBay. So this was only the first one that came up.

https://www.ebay.com/itm/116367606865

 

[praezis]

On 3/14/2025 at 2:53 AM, RickTock said:

Barrel Diameter: 8.5

So this was a very misleading statement. In fact it is the container ring diameter. 

[mikepilk]

59 minutes ago, praezis said:

So this was a very misleading statement. In fact it is the container ring diameter. 

It's a misleading world out there Frank . You wouldn't believe the crap some people are saying, despite them being the leader of their country