How do you choose a mainspring?

[graemeW]

I have 2 of these movements. I just put together the good one, with a couple of bits from the other. It's running ok considering the mainspring is very tired! They both have identical main springs, so I presume they are the 100 year old originals.

I don't know what the movement is, no markings.

The spring is 1.6mm high, 0.15mm thick, 280mm long. Barrel is 11.5mm diameter and the arbor is 3.7mm.

I can't find anything that seems even close enough to have a stab at.

It looks like I might have to go down on thickness and up on length.

1.6, 0.135, 340, 11 maybe?

The same is available in 0.14 too. Which would work better with the extra 60mm length?

I don't know what the arbor loop size is on these though, they are gr4577 and gr4588

I can go 0.13 300 to, gr4562.

None of them jump out at me as ideal though. How far from spec can you get away with? 

[RichardHarris123]

The most important factors are hight and strength.  Strength wise, modern springs are stronger so you definitely don't want to go up. I'll have a look see what I can find.  What sort of bridal do you need? 

[tomh207]

Have a look at these too Graeme 

Tom

[graemeW]

4 minutes ago, RichardHarris123 said:

The most important factors are hight and strength.  Strength wise, modern springs are stronger so you definitely don't want to go up. I'll have a look see what I can find.  What sort of bridal do you need? 

It's non automatic and just has another bit of spring on the eng to catch the tab on the wall. I don't know the terms, does that make sense?

[RichardHarris123]

Closest I can find.  Where are you located? 

Just seen, you've already mentioned this one, should be fine. 

[graemeW]

1 minute ago, RichardHarris123 said:

Closest I can find.  Where are you located? 

Just seen, you've already mentioned this one, should be fine. 

I'm uk.

Yes, I think gr4588 will be my best bet. Thanks.