Elgin Factory Mainspring for MST caliber 281 & Certina caliber 201 - No. 6709 - Alloy

Elgin Factory Mainspring No. 6709, for MST caliber 281 & Certina caliber 201 and probably a very obscure Elgin grade somewhere, (tongue) end, alloy, new in envelope. I don't see an Elgin grade that's based on either of these movements. See images for precise specifications. I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do a satisfactory job of representing the item