FOR SALE IS A WATCH MAINSPRING  (1)  New Old Stock These are standard mainsprings First quality with the standard tongue end unless noted otherwise-see package for details. Sizeing with reference to the mainspring gauge pictured, the measurements listed may be dennison or metric. read the label usually both. 1st number width. ( mm or Den) second number thickness ( Strength mm or Den)   third number length. (usually inches) . The strength is determine by sliding the old mainspring down the silver part of the gauge and reading. one side of gauge is mm the other dennision. OR using the Bestfit catalog looking up the size for the watch movement. Most spring are sealed and never opened some opened and inspected. If in dought please email NO I don't look up mainsprings I sell them . I do repair watches still .