I have a 1958 Seamaster automatic and I can't figure out what size of strap to buy. Here is a picture of the inside case, if that helps.

 

Measure the gap between the lugs, It should be 18 millimetres.

Here is a 2846 describing the band.

Thanks @tomvox1

 

Thank you for the link and information. Is there a way to figure out the exact strap this watch came with from Omega? When I bought it, it had a cheap after-market strap.

Thanks.

 

Look for old advertisements to get an idea, but most straps look like pig skin and you need a 18 mm as stated.

Length? depends on your wrist size

DON